Activated PI3K delta syndrome (APDS) is characterized by a spectrum of clinical manifestations involving the immune system leading to increased susceptibility to infections (e.g., otitis media, sinusitis, bronchitis, and pneumonia), autoimmune/autoinflammatory manifestations including autoimmune cytopenias, gastrointestinal manifestations resembling Crohn-like colitis, intussusception, and lymphoproliferation (e.g., lymphadenopathy, hepatosplenomegaly, and nodular lymphoid hyperplasia), and an increased risk of developing B-cell lymphomas and other malignancies. Short stature, growth delays, and neurodevelopmental delays are also reported. APDS type 1 (APDS1) is caused by a heterozygous pathogenic gain-of-function variant in PIK3CD, and APDS type 2 (APDS2) is caused by a heterozygous loss-of-function pathogenic variant in PIK3R1. The key clinical differences between APDS1 and APDS2 include short stature, frequency of gastrointestinal infections, and characteristic dental findings, which are more prominent in APDS2.The clinical diagnosis of APDS can be established in a proband based on suggestive clinical findings, or the molecular diagnosis can be established in a proband with suggestive findings and a heterozygous pathogenic variant in PIK3CD (for APDS1) or PIK3R1 (for APDS2) identified by molecular genetic testing.Targeted therapies: Leniolisib, a selective PI3K delta (PI3Kδ) inhibitor, has shown promise in clinical trials by directly targeting the overactive PI3Kδ signaling pathway, a hallmark of the condition, and is therefore recommended as a first-line treatment of significant lymphoproliferative disease, including lymphadenopathy and splenomegaly. Sirolimus, an inhibitor of the mammalian target of rapamycin (mTOR), is recommended for individuals with lymphoproliferative disease or organomegaly when leniolisib is unavailable; it is also used off-label due to its immunosuppressive and antiproliferative properties. Allogenic hematopoietic stem cell transplant (HSCT) is reserved for individuals with severe or treatment-refractory APDS, including progressive organ damage, recurrent refractory infections, or severe immune dysregulation unresponsive to pharmacologic therapy. Supportive care: Regular intravenous or subcutaneous immunoglobulin replacement therapy to prevent recurrent bacterial infections and improve immune function; long-term prophylactic antibiotics can be considered to reduce the frequency of bacterial infections; individuals with recurrent herpes simplex or herpes zoster virus can receive prophylactic acyclovir or valganciclovir. Leniolisib or sirolimus targeted therapies for lymphoproliferation. Glucocorticoids for acute management of autoimmune complications; other immunosuppressive agents for chronic management of autoimmune manifestations. Bronchodilators and inhaled steroids for chronic lung disease; pulmonary hygiene and preventative pulmonary care to decrease risk of respiratory infections. Nutritional support and dietary modifications for gastrointestinal manifestations; anti-inflammatory medications including high-dose glucocorticoids for treatment of inflammatory bowel disease (which may also improve gut function and enhance absorption of targeted therapies); consider assisted enteral/parenteral nutrition for severe cases. Developmental interventions and educational support to address developmental delays and cognitive impairments. Offer counseling to address psychosocial impacts. Surveillance: Annually assess infection risk (blood/sputum cultures for EBV, CMV, and HSV), immune function (immunoglobulin levels, CD4+, CD8+, B-cell subsets, response to vaccines), lymphoproliferative status (CBC, B-cell counts), autoimmunity (ANA screen, TSH, TPO), respiratory function (including pulmonary function tests), and gastrointestinal status (liver function tests); CT or MRI of the chest every three to five years; colonoscopy symptomatically as needed; liver ultrasound at baseline and every two to three years; psychiatric assessments as needed. Evaluation of relatives at risk: Molecular genetic testing for the APDS pathogenic variant identified in the proband is recommended for all at-risk relatives in order to identify as early as possible those who would benefit from prompt initiation of treatment and preventive measures. Detailed clinical and laboratory evaluations to assess for possible clinical features related to APDS is recommended for family members found to have an APDS pathogenic variant.APDS is an autosomal dominant disorder. Approximately 80% of individuals diagnosed with APDS have an affected parent and 20% of individuals have the disorder as the result of a de novo PIK3CD gain-of-function variant (for APDS1) or de novo PIK3R1 loss-of-function variant (for APDS2). Once the PIK3CD or PIK3R1 pathogenic variants have been identified in an affected family member, carrier testing for at-risk relatives and prenatal/preimplantation genetic testing are possible.Copyright © 1993-2025, University of Washington, Seattle. GeneReviews is a registered trademark of the University of Washington, Seattle. All rights reserved.

Hepatic veno-occlusive disease with immunodeficiency (VODI) is characterized by (1) combined immunodeficiency and (2) terminal hepatic lobular vascular occlusion and hepatic fibrosis manifesting as hepatomegaly and/or hepatic failure. Onset is usually before age six months. The immunodeficiency comprises severe hypogammaglobulinemia, clinical evidence of T-cell immunodeficiency with normal numbers of circulating T and B cells, absent lymph node germinal centers, and absent tissue plasma cells. Bacterial and opportunistic infections including Pneumocystis jirovecii infection, mucocutaneous candidiasis, and enteroviral or cytomegalovirus infections occur. In the past the prognosis for affected individuals was poor, with 100% mortality in the first year of life if unrecognized and untreated with intravenous or subcutaneous immunoglobulin (IVIG/SCIG) and Pneumocystis jirovecii prophylaxis. However, with early recognition and treatment, including the more recent use of defibrotide, there is a marked improvement in prognosis. Early hematopoietic stem cell transplantation (HSCT) using non-hepatoxic drugs in conditioning and prophylactic defibrotide is potentially curative.The diagnosis of VODI is established in a proband who meets clinical diagnostic criteria or by identification of biallelic pathogenic variants in SP110 on molecular genetic testing.Targeted therapies: IVIG/SCIG; defibrotide for acute hepatic disease; HSCT with non-hepatotoxic conditioning therapy, preferably with defibrotide prophylaxis. Supportive care:Pneumocystis jirovecii prophylaxis; prompt treatment of infections with antibacterials, antivirals, or antifungals as indicated; standard treatment for complications of liver disease; consider liver transplantation, although rate of complications may be high. Surveillance: Assess growth every three to six months; measurement of immunoglobulin concentrations every three to six months; bronchoalveolar lavage to diagnose Pneumocystis jirovecii infection; viral and bacterial cultures and PCR as needed; serum aminotransferases, bilirubin, albumin, complete blood count, and platelet count every three to six months; pulmonary function studies annually once able to perform reliably; cerebrospinal imaging to identify leukodystrophy or other central nervous system pathology when clinically indicated. Agents/circumstances to avoid: Agents known to predispose to hepatic veno-occlusive disease including cyclophosphamide and Senecio alkaloids / bush teas. Evaluation of relatives at risk: If both pathogenic variants in the family are known, it is appropriate to evaluate via molecular genetic testing sibs of a proband who are younger than age 12 months in order to identify those who would benefit from initiation of IVIG or SCIG treatment, Pneumocystis jirovecii prophylaxis, and consideration of preemptive HSCT.VODI is inherited in an autosomal recessive manner. If both parents are known to be heterozygous for an SP110 pathogenic variant, each sib of an affected individual has at conception a 25% chance of being affected, a 50% chance of being an asymptomatic carrier, and a 25% chance of being unaffected and not a carrier. Once the SP110 pathogenic variants have been identified in an affected family member, carrier testing for at-risk relatives and prenatal/preimplantation genetic testing for VODI are possible.Copyright © 1993-2025, University of Washington, Seattle. GeneReviews is a registered trademark of the University of Washington, Seattle. All rights reserved.

Spinal muscular atrophy (SMA) is characterized by muscle weakness and atrophy resulting from progressive degeneration and irreversible loss of the anterior horn cells in the spinal cord (i.e., lower motor neurons) and the brain stem nuclei. The onset of weakness ranges from before birth to adulthood. The weakness is symmetric, proximal greater than distal, and progressive. Before the genetic basis of SMA was understood, it was classified into clinical subtypes based on maximum motor function achieved; however, it is now apparent that the phenotype of SMN1-associated SMA spans a continuum without clear delineation of subtypes. With supportive care only, poor weight gain with growth failure, restrictive lung disease, scoliosis, and joint contractures are common complications; however, newly available targeted treatment options are changing the natural history of the disease.The diagnosis of SMA is established in a proband with a history of motor difficulties or regression, proximal muscle weakness, reduced/absent deep tendon reflexes, evidence of motor unit disease, and/or biallelic pathogenic variants in SMN1 identified by molecular genetic testing. Increases in SMN2 copy number often modify the phenotype.Targeted therapies: Therapies targeted to the underlying disease mechanism include risdiplam (Evrysdi®; SMN2-directed RNA splicing modifier), nusinersen (Spinraza®; antisense oligonucleotide), and onasemnogene abeparvovec-xioi (Zolgensma®; gene replacement therapy) for the treatment of all types of SMA. Treatment with an SMA-specific disease-modifying treatment is most efficacious when initiated presymptomatically. The FDA has issued a black box warning about Zolgensma®, noting the possibility of serious liver injury and acute liver failure; close monitoring of liver function prior to and in the months following infusion is indicated. These targeted treatments may prevent the development or slow the progression of some features of SMA. New phenotypes in treated individuals are arising, and long-term effects of these treatments are unknown. Supportive care: Proactive supportive treatment by a multidisciplinary team is essential to reduce symptom severity, particularly in the most severe cases of SMA and/or in untreated individuals. When nutrition or dysphagia is a concern, placement of a gastrostomy tube early in the course of the disease is appropriate. Standard therapy for gastroesophageal reflux disease and chronic constipation is recommended. Formal consultation and frequent follow up with a pulmonologist familiar with SMA is necessary. As respiratory function deteriorates, tracheotomy or noninvasive respiratory support may be offered. Surgical repair for scoliosis should be considered based on progression of the curvature, pulmonary function, and bone maturity. Surgical intervention for hip dislocation for those with pain may be indicated. Surveillance: Individuals with SMA require monitoring for the development of symptoms to determine appropriate timing to initiate supportive therapies. Surveillance recommendations for potential side effects and new phenotypes associated with the targeted treatments are emerging. Multidisciplinary evaluation every six months or more frequently for weaker children is indicated to assess nutritional state, respiratory function, motor function, and orthopedic status, and to determine appropriate interventions. Agents/circumstances to avoid: Prolonged fasting, particularly in the acutely ill infant with SMA. Evaluation of relatives at risk: It is appropriate to determine the genetic status of younger, apparently asymptomatic sibs of an affected individual in order to identify as early as possible those who would benefit from prompt initiation of disease-modifying treatments. Pregnancy management: Women with SMA may have an increased rate of preterm birth and need for cesarean section compared to unaffected women. Women with SMA may also experience a persistent worsening of their general muscle weakness after delivery, particularly if disease-modifying therapies are discontinued due to pregnancy status. Due to the risk of respiratory failure, it is recommended that women with neuromuscular disorders, including those with SMA, obtain baseline pulmonary function prior to becoming pregnant, with frequent monitoring during pregnancy. There is limited to no data on the effects of disease-modifying treatments on the developing human fetus. However, based on animal models, risdiplam use should be avoided in pregnant women.SMA is inherited in an autosomal recessive manner. Each pregnancy of a couple who have had a child with SMA has an approximately 25% chance of producing an affected child, an approximately 50% chance of producing an asymptomatic carrier, and an approximately 25% chance of producing an unaffected child who is not a carrier. These recurrence risks deviate slightly from the norm for autosomal recessive inheritance because about 2% of affected individuals have a de novoSMN1 pathogenic variant on one allele; in these instances, only one parent is a carrier of an SMN1 variant, and thus the sibs are not at increased risk for SMA. Ideally preconception (but also prenatal) carrier testing for all individuals in the general population and prenatal testing for pregnancies at increased risk are possible if the diagnosis of SMA has either been confirmed by molecular genetic testing in an affected family member and/or if both parents are found to be carriers of SMA on carrier screening testing.Copyright © 1993-2025, University of Washington, Seattle. GeneReviews is a registered trademark of the University of Washington, Seattle. All rights reserved.

The WAS-related disorders, which include Wiskott-Aldrich syndrome, X-linked thrombocytopenia (XLT), and X-linked neutropenia (XLN), are a spectrum of disorders of hematopoietic cells, with predominant defects of platelets and lymphocytes. Wiskott-Aldrich syndrome usually presents in infancy. Affected males have thrombocytopenia with intermittent mucosal bleeding, bloody diarrhea, and intermittent or chronic petechiae and purpura; recurrent bacterial, viral, fungal, and/or opportunistic infections; and eczema. Approximately 25%-40% of those who survive the early complications develop one or more autoimmune conditions including hemolytic anemia, immune thrombocytopenic purpura, immune-mediated neutropenia, vasculitis, rheumatoid arthritis, and immune-mediated damage to the kidneys and liver. Individuals with a WAS-related disorder, particularly those who have been exposed to Epstein-Barr virus (EBV), are at increased risk of developing lymphomas, which often occur in unusual extranodal locations including the brain, lung, or gastrointestinal tract. Males with XLT have small platelet volume and thrombocytopenia. Severe disease-related events include severe bleeding episodes (14%), autoimmunity (12%), life-threatening infections (7%), and malignancy (5%). Males with XLN typically have congenital neutropenia associated with myelodysplasia, hyperactive neutrophils, increased myeloid cell apoptosis, and lymphoid cell abnormalities.The diagnosis of a WAS-related disorder is established in a male proband with both congenital thrombocytopenia (<70,000 platelets/mm3) and small platelets; at least one of the following features: eczema, recurrent bacterial, viral, and fungal infections, autoimmune disease(s), malignancy, reduced WASP expression in a fresh blood sample, abnormal antibody response to polysaccharide antigens and/or low isohemagglutinins, or positive maternal family history of a WAS-related disorder; and a hemizygous WAS pathogenic variant identified by molecular genetic testing (necessary to confirm the diagnosis). The diagnosis of a WAS-related disorder in a female is uncommon. It is usually established by identification of a heterozygous pathogenic variant in WAS by molecular genetic testing in a female with severe skewed X-chromosome inactivation and increased expression of the mutated WAS allele.Targeted therapy: The only curative targeted therapy clinically available for Wiskott-Aldrich syndrome is allogeneic hematopoietic stem cell transplantation (HSCT). In those with XLT, decision to treat with HSCT is determined on an individual basis. Treatment of manifestations: In those with Wiskott-Aldrich syndrome and XLT, treatment is individualized based on disease manifestations and includes management of thrombocytopenia; prevention of infection with immunoglobulin replacement; topical steroids for eczema; antibiotics as needed for chronic skin infections; prophylactic antibiotics for Pneumocystis jirovecii in infants with Wiskott-Aldrich syndrome; intravenous immunoglobulin G; routine non-live immunizations; prompt evaluation and treatment for infection including empiric parenteral antibiotics and exhaustive search for source of infection; and judicious use of immunosuppressants for autoimmune disease prior to definitive treatment. In those with XLN, treatment includes granulocyte colony-stimulating factor therapy; routine non-live immunizations; prompt evaluation and treatment for infection including empiric parenteral antibiotics and exhaustive search for source of infection; and treatment of myelodysplastic syndrome and acute myelogenous leukemia per hematologist/oncologist. Surveillance: Complete blood count including platelet count and size and assessment for complications associated with increased bleeding as recommended by hematologist; annual skin examination; assessment by immunologist including for recurrent infections with frequency as recommended by immunologist; annual clinical assessment for autoimmune dysfunction and for manifestations of lymphoma. Agents/circumstances to avoid: Circumcision of at-risk newborn males who have thrombocytopenia; use of medications that interfere with platelet function. Defer elective procedures until after HSCT. Evaluation of relatives at risk: Evaluation of at-risk newborn males so that morbidity and mortality can be reduced by early diagnosis and treatment. Evaluation of relatives considering stem cell donation to inform transplant donor decision making.WAS-related disorders are inherited in an X-linked manner. If the mother of the proband has a WAS pathogenic variant, the chance of transmitting it in each pregnancy is 50%. Males who inherit the pathogenic variant will be symptomatic. Females who inherit the pathogenic variant will be carriers and are typically asymptomatic. Males with a WAS-related disorder transmit the pathogenic variant to all of their daughters and none of their sons. Once the WAS pathogenic variant has been identified in a family member, molecular genetic testing to identify female heterozygotes and prenatal and preimplantation genetic testing are possible.Copyright © 1993-2025, University of Washington, Seattle. GeneReviews is a registered trademark of the University of Washington, Seattle. All rights reserved.

The clinical phenotype of alpha-mannosidosis varies considerably, with a wide spectrum of clinical findings and broad variability in individual presentation. At least three clinical types have been suggested in untreated individuals: mild (clinically recognized after age ten years, with myopathy, slow progression, and absence of skeletal abnormalities); moderate (clinically recognized before age ten years, with myopathy, slow progression, and presence of skeletal abnormalities); and severe (obvious progression leading to early death from primary central nervous system involvement or infection). Core features of untreated individuals generally include early childhood-onset non-progressive hearing loss, frequent infections due to immunodeficiency, rheumatologic symptoms (especially systemic lupus erythematosus), developmental delay / intellectual disability, low tone, ataxia, spastic paraplegia, psychiatric findings, bone disease (ranging from asymptomatic osteopenia to focal lytic or sclerotic lesions and osteonecrosis), gastrointestinal dysfunction (including diarrhea, swallowing issues / aspiration, and enlarged liver and spleen), poor growth, eye issues (including tapetoretinal degeneration and optic nerve atrophy), cardiac complications in adults, and pulmonary issues (including parenchymal lung disease). However, with the advent of enzyme replacement therapy, the natural history of this condition may change. Long-term velmanase alfa (VA) treatment outcomes are still being elucidated, but may include improvement in hearing, immunologic profile, and quality of life (improved clinical outcomes for muscle strength). Similarly, affected individuals who underwent hematopoietic stem cell transplantation (HSCT) experienced improvement in development (with preservation of previously learned skills), ability to participate in activities of daily living, stabilization or improvement in skeletal abnormalities, and improvement in hearing ability, although expressive speech and hearing deficiencies remained the most significant clinical problems after HSCT.The diagnosis of alpha-mannosidosis is established in a proband by identification of deficiency of lysosomal enzyme acid alpha-mannosidase (typically 5%-10% of normal activity) in leukocytes or other nucleated cells AND/OR by the identification of biallelic pathogenic variants in MAN2B1 by molecular genetic testing.Targeted therapies: Velmanase alfa (Lamzede®) enzyme replacement therapy (ERT) has been very well tolerated and is now regarded as a standard treatment for alpha-mannosidosis; improvement in both biochemical and functional parameters have been reported in treated individuals. Hematopoietic stem cell transplantation (HSCT) has been offered as a treatment for severe alpha-mannosidosis. While HSCT carries risks, the data suggests it is a feasible therapeutic option for alpha-mannosidosis, with better outcomes achieved by performing it early before complications arise, balancing the risks and benefits. Supportive care: Hearing aids may be helpful for those with sensorineural hearing loss, whereas pressure-equalizing tubes may be helpful for those with conductive hearing loss. Consider palmidronate (Aredia®) monthly or zoledronic acid (Aclasta®) once a year for osteoporosis or osteopenia. Standard treatment for immunodeficiency / recurrent infections, systemic lupus erythematosus, communicating hydrocephalus, ataxia / gait abnormalities, poor weight gain / growth issues, eye/vision issues, cardiac valve dysfunction / dilated cardiomyopathy, recurrent chest infections / respiratory dysfunction, developmental delay / intellectual disability, and psychiatric manifestations. Surveillance: At each visit, measure weight, length/height, head circumference, and BMI; monitor growth pattern, developmental progress, and educational needs; assess for depression, including sleep disturbances, anxiety, &/or findings suggestive of psychosis; assess for new manifestations such as ataxia and gait abnormalities; evaluate for asthenia and signs/symptoms of communicating hydrocephalus; assess for muscle pain, joint aches, reduced range of motion, and bone pain; monitor for diarrhea and for size of the liver and spleen; and assess for the number and type of infections. Every six to 12 months in childhood and annually in adults, assess fine motor function, gross motor function, endurance, and muscle strength and tone by physical therapy; and assess for features of ataxia. Every one to two years, or as clinically indicated in those with hearing aids, perform an audiology evaluation. Every two to five years in children, adolescents, and adults, consider DXA bone densitometry scan to assess for osteopenia or osteoporosis; radiographs of the hips/spine may be indicated. Annually (or as clinically indicated), routine biochemical lab assessment to include liver and kidney health, blood glucose levels, fluid and electrolyte balance, and complete blood count (with platelets); consider immunlobulin levels, ESR and C-reactive protein; pulmonary function tests; and ophthalmology evaluation. At regular intervals based on clinical features, consider endocrinology evaluations, including hormonal and lipid profiles; consider assessment of liver and spleen size through ultrasound or MRI imaging; consider electrocardiogram, 24-hour electrocardiogram, and echocardiogram; consider sleep study. For those on ERT, plasma oligosaccharides to assess treatment response as clinically indicated. Post-HSCT evaluation of standard surveillance per hematologist/oncologist, which may include ongoing assessment for chimerism and enzyme activity if indicated. Evaluation of relatives at risk: Testing of all at-risk sibs of any age (including prenatal diagnosis) is warranted to allow for early diagnosis and targeted treatment of alpha-mannosidosis. Evaluations can include molecular genetic testing if the pathogenic variants in the family are known or assay of acid alpha-mannosidase enzyme activity in leukocytes or other nucleated cells if the pathogenic variants in the family are not known.Alpha-mannosidosis is inherited in an autosomal recessive manner. At conception, each sib of an affected individual has a 25% chance of being affected, a 50% chance of being an asymptomatic carrier, and a 25% chance of being unaffected and not a carrier. Carrier testing for at-risk relatives is possible if the pathogenic variants in the family are known. Prenatal testing for a pregnancy at increased risk is possible by assay of acid alpha-mannosidase enzymatic activity or molecular genetic testing once the pathogenic variants have been identified in the family.Copyright © 1993-2025, University of Washington, Seattle. GeneReviews is a registered trademark of the University of Washington, Seattle. All rights reserved.

Familial hemophagocytic lymphohistiocytosis (fHLH), defined as the presence of biallelic pathogenic variants in one of four genes (PRF1, STX11, STXBP2, or UNC13D), is an immune deficiency characterized by the overactivation and excessive proliferation of T lymphocytes and macrophages, leading to infiltration and damage of organs including the bone marrow, liver, spleen, and brain. Familial HLH usually presents as an acute illness with prolonged and high fever, cytopenias, and hepatosplenomegaly. Rash and lymphadenopathy are less common. Individuals with fHLH may also exhibit liver dysfunction and neurologic abnormalities. Although manifestations of fHLH are usually evident within the first months or years of life and may develop in utero, symptomatic presentation can occur throughout childhood and into adulthood. Median survival in untreated infants with fHLH who develop active disease is less than two months after onset of manifestations; progressive manifestations of fHLH, organ dysfunction, invasive infection, and bleeding account for the majority of deaths. However, the use of newer chemoimmunotherapy protocols followed by allogeneic hematopoietic stem cell transplantation (HSCT) has improved survival.The diagnosis of fHLH is established in a proband with suggestive findings by identification of either biallelic pathogenic variants in one of four genes (PRF1, STX11, STXBP2, or UNC13D) or (rarely) a gain-of-function heterozygous variant in STXBP2.Targeted therapies: Treatment regimens focus on use of chemoimmunotherapy to treat active disease followed by allogeneic HSCT, the only curative therapy. Etoposide-containing regimens such as HLH-94 and HLH-2004, followed by allogeneic HSCT, are typically used. A regimen that includes anti-interferon-gamma antibody (emapalumab) is FDA approved for the treatment of children and adults with relapsed or refractory HLH or intolerance of conventional therapies. Supportive care: Management should be coordinated by or in consultation with a multidisciplinary team with expertise in fHLH, including specialists in hematology/oncology, bone marrow and stem cell transplantation, immunology, rheumatology, infectious diseases, critical care, neurology, nephrology, pathology, and medical genetics. Supportive care that should accompany treatment with chemoimmunotherapy and allogenic HSCT includes antibiotics or antiviral agents to treat or prevent infections, and antipyretics, intravenous fluids, electrolyte replacement, transfusion of packed red blood cells and platelets, infusions of immunoglobulin, fresh frozen plasma, and/or cryoprecipitate. Surveillance: Individuals responding to treatment and HSCT are technically not at risk for other organ system involvement; thus, surveillance focuses on potential complications of fHLH while fHLH is active, such as bleeding, hypotension, respiratory distress, neurologic complications, malnutrition, infection, liver, or other organ failure. Agents/circumstances to avoid: Live vaccines; exposure to infections; acetaminophen in persons with liver failure; nonsteroidal anti-inflammatory drugs in persons with thrombocytopenia; areas of construction or soil manipulation (which increase the risk for fungal infection in individuals with neutropenia); transfusion of non-irradiated blood products in individuals undergoing chemoimmunotherapy and/or allogeneic HSCT. Evaluation of relatives at risk: It is appropriate to identify – before symptoms occur –those at-risk sibs who have the family-specific pathogenic variants so that they can be monitored and preemptive HSCT considered (particularly during febrile episodes) for development of manifestations of active disease. Any manifestations of possible active disease should prompt more detailed evaluation and referral to a clinician with expertise in fHLH.Familial HLH is inherited in an autosomal recessive manner. (Autosomal dominant inheritance of STXBP2-fHLH is suggested by rare reports of symptomatic individuals with heterozygous gain-of-function variants. Autosomal dominant inheritance will not be discussed further in this section.) If both parents are known to be heterozygous for an fHLH-causing pathogenic variant, each sib of an affected individual has a 25% chance of inheriting biallelic pathogenic variants, a 50% chance of inheriting one pathogenic variant and being an asymptomatic carrier, and a 25% chance of inheriting neither of the familial fHLH-causing pathogenic variants. Once the fHLH-causing pathogenic variants have been identified in an affected family member, carrier testing for at-risk relatives and prenatal and preimplantation genetic testing are possible.Copyright © 1993-2025, University of Washington, Seattle. GeneReviews is a registered trademark of the University of Washington, Seattle. All rights reserved.

X-linked infantile spinal muscular atrophy (XL-SMA) is characterized by congenital hypotonia, areflexia, and evidence of degeneration and loss of anterior horn cells (i.e., lower motor neurons) in the spinal cord and brain stem. Often congenital contractures and/or fractures are present. Intellect is normal. Life span is significantly shortened because of progressive ventilatory insufficiency resulting from chest muscle involvement.The diagnosis of X-linked infantile spinal muscular atrophy is established in a male proband with suggestive clinical features and a hemizygous pathogenic variant in UBA1 identified by molecular genetic testing.Treatment of manifestations: Assure adequate caloric intake by caloric supplementation and/or gastrostomy feedings; manage constipation with diet or medication; provide rigorous airway clearance techniques, secretion management, and, ideally, noninvasive ventilatory support, although tracheostomy with permanent mechanical ventilation can be considered; discuss "do not attempt to resuscitate" status with the family before respiratory failure occurs. Orthopedic consultation and physical and occupational therapy to manage contractures and progressive scoliosis. Standard treatment for gastroesophageal reflux disease. Surveillance: Affected children should be followed at least monthly until the severity and disease course are more clearly delineated. Routine evaluations by a multidisciplinary team, including neurology, pulmonology, orthopedics, physical and occupational therapy, nutrition, and gastroenterology, as needed. Measurement of growth parameters, neurologic evaluation, nutrition/feeding assessment, evaluation of respiratory status, and physical examination for kyphosis/scoliosis at each visit.By definition, XL-SMA is inherited in an X-linked manner. Heterozygous females have a 50% chance of transmitting the pathogenic variant with each pregnancy. Males who inherit the pathogenic variant will be affected; females who inherit the pathogenic variant will be heterozygotes and will usually not be affected. Once the UBA1 pathogenic variant has been identified in an affected family member, carrier testing for at risk female relatives and prenatal and preimplantation genetic testing are possible.Copyright © 1993-2025, University of Washington, Seattle. GeneReviews is a registered trademark of the University of Washington, Seattle. All rights reserved.

Arylsulfatase A deficiency (also known as metachromatic leukodystrophy or MLD) is characterized by three clinical subtypes: late-infantile, juvenile, and adult MLD. The age of onset within a family is usually similar. The disease course may be from several years in the late-infantile-onset form to decades in the juvenile- and adult-onset forms. Late-infantile MLD: Onset is before age 30 months. Typical presenting findings include weakness, hypotonia, clumsiness, frequent falls, toe walking, and dysarthria. Language, cognitive, and gross and fine motor skills regress as the disease progresses. Later signs include spasticity, pain, seizures, and compromised vision and hearing. In the final stages, children have tonic spasms, decerebrate posturing, and general unawareness of their surroundings. Juvenile MLD: Onset is between age 30 months and 16 years. Initial manifestations include a decline in school performance and the emergence of behavioral problems, followed by gait disturbances. Progression is similar to but slower than in the late-infantile form. Adult MLD: Onset occurs after the age of 16 years, sometimes not until the fourth or fifth decade. Initial signs can include problems in school or job performance, personality changes, emotional lability, or psychosis; in others, neurologic symptoms (weakness and loss of coordination progressing to spasticity and incontinence) or seizures predominate initially. Peripheral neuropathy is common. The disease course is variable, with periods of stability interspersed with periods of decline, and may extend over two to three decades. The final stage is similar to earlier-onset forms.The diagnosis of MLD is established in a proband with the suggestive findings of progressive neurologic dysfunction, brain MRI evidence of leukodystrophy, or arylsulfatase A enzyme deficiency by identification of biallelic ARSA pathogenic variants on molecular genetic testing, elevated urinary excretion of sulfatides, or – less commonly – metachromatic lipid deposits in nervous system tissue.Targeted therapy: Allogeneic hematopoietic stem cell transplantation (HSCT) can treat primary central nervous system manifestations in those with pre- and very early-symptomatic juvenile- or adult-onset MLD. Autologous HSCT using gene-modified hematopoietic stem cells (also known as ex vivo gene therapy) is approved in the United States, European Union, and United Kingdom for individuals with presymptomatic late-infantile MLD, presymptomatic early-onset juvenile MLD, or early-symptomatic early-onset juvenile MLD with maintained ability to walk and before the onset of cognitive decline. Supportive care: Developmental and educational support. Treatment per orthopedist, physical medicine and rehabilitation, and physical and occupational therapists to avoid contractures and falls and maintain neuromuscular function and mobility, muscle relaxants for contractures, and safety measures for gait or movement limitations. Feeding therapy, swallowing aids, suction equipment, and other standard treatments for drooling, swallowing difficulty, and gastroesophageal reflux. Gastrostomy tube as needed for feeding. Treatment of seizures using anti-seizure medications in standard protocols. Standard treatments for impaired vison and/or hearing and respiratory issues. Family support to enable parents and/or caregivers to anticipate decisions on walking aids, wheelchairs, feeding tubes, and other changing care needs. Surveillance: Brain MRI examination to monitor the status of demyelination using MLD brain MRI severity scoring with frequency per neurologist. Assess motor function and support needs using gross motor function measurement (GMFM). Monitor for disease exacerbations following febrile infections. At each visit, assess physical mobility, self-help skills, development, neurobehavioral and psychiatric issues, growth, nutrition, safety of oral intake, need for feeding support, constipation, respiratory issues, and family needs. Vision and hearing assessment as needed.MLD is inherited in an autosomal recessive manner. At conception, each sib of an affected individual has a 25% chance of being affected, a 50% chance of being an asymptomatic carrier, and a 25% chance of being unaffected and not a carrier. Carrier testing of at-risk family members and prenatal testing for a pregnancy at increased risk are possible if both ARSA pathogenic variants have been identified in an affected family member.Copyright © 1993-2025, University of Washington, Seattle. GeneReviews is a registered trademark of the University of Washington, Seattle. All rights reserved.

Adenosine deaminase (ADA) deficiency is a systemic purine metabolic disorder that primarily affects lymphocyte development, viability, and function. The ADA deficiency phenotypic spectrum includes typical early-onset severe combined immunodeficiency (ADA-SCID), diagnosed in infancy (about 80% of individuals), and less severe "delayed" or "late-onset" combined immunodeficiency (ADA-CID), diagnosed in older children and adults (15%-20% of individuals). Some healthy individuals who are deficient in red blood cell ADA (termed "partial ADA deficiency") have been discovered by screening populations or relatives of individuals with ADA-SCID. Newborn screening (NBS) for SCID uses extracts from Guthrie card dried blood spots to measure T-cell receptor excision circle (TREC) DNA by polymerase chain reaction (PCR). Screening specific for ADA deficiency can also be performed by detection of elevated levels of adenosine (Ado) and deoxyadenosine (dAdo) by tandem mass spectrometry (TMS). Both techniques can identify ADA-SCID before affected infants become symptomatic. Untreated ADA-SCID presents as life-threatening opportunistic illnesses in the first weeks to months of life with poor linear growth and weight gain secondary to persistent diarrhea, extensive dermatitis, and recurrent pneumonia. Skeletal abnormalities affecting ribs and vertebra, pulmonary alveolar proteinosis, hemolytic anemia, neurologic abnormalities, and transaminitis may also suggest untreated ADA-SCID. Characteristic immune abnormalities are lymphocytopenia (low numbers of T, B, and NK cells) combined with the absence of both humoral and cellular immune function. If immune function is not restored with enzyme replacement therapy (ERT), gene therapy, or hematopoietic stem cell transplantation (HSCT), children with ADA-SCID rarely survive beyond age one to two years. NBS for SCID does not identify individuals with the ADA-CID phenotype whose TREC numbers are above the threshold values of most screening laboratories. However, ADA-CID is identified by TMS NBS since the ADA substrates Ado and dAdo are increased. As TMS NBS for Ado/dAdo is not yet widely performed, individuals with ADA-CID are more often clinically diagnosed between ages one and ten years ("delayed" onset), or less often in the second to fourth decades ("late"/"adult" onset). Because the immunologic abnormalities are less pronounced than those of ADA-SCID, infections in ADA-CID may not be life-threatening and include recurrent otitis media, sinusitis, upper respiratory infections, and human papilloma viral infections. Untreated individuals with ADA-CID can develop over time chronic pulmonary disease, autoimmunity, atopic disease with elevated immunoglobulin E, and malignancy.The diagnosis of ADA deficiency is established in a proband with suggestive findings either by biochemical testing showing <1% of ADA catalytic activity in red blood cells or in extracts of dried blood spots (valid in untransfused individuals), or by molecular genetic testing identifying biallelic pathogenic variants in ADA. Frequently, both types of testing are performed.Treatment of manifestations: Newborns with an abnormal NBS result suggestive of ADA-SCID (by either method) require immediate protection from risk factors for infection and referral for a subspecialty immunology evaluation at a center with expertise in both diagnosis of SCID and its genetic causes and SCID treatment protocols. Symptomatic treatment involves treatment of infections and use of immunoglobulin infusions and antibiotics, particularly prophylaxis against Pneumocystis jirovecii pneumonia (formerly Pneumocystis carinii) and fungal infections. Prophylaxis against viral infections depends upon exposure and requires frequent surveillance via viral PCR-based testing, with appropriate targeted virus-specific therapy if present. Targeted therapies: Correcting the ADA deficiency either systemically or selectively in lymphoid cells employs one of three options: (1) enzyme replacement therapy (ERT) by intramuscular administration of PEGylated ADA, (2) allogeneic HSCT, or (3) autologous hematopoietic stem cell ADA gene therapy (HSC-GT) – the latter two are curative. Often, ERT is initiated first to rapidly correct the metabolic defect and to protect against serious infections as well as neurologic/behavioral abnormalities. It is discontinued at the time HSCT or HSC-GT is performed. Surveillance: The following evaluations are recommended to monitor existing and emerging clinical manifestations and the response to targeted treatment and supportive care: (1) absolute lymphocyte subset counts (T, B, NK cells), quantitative serum immunoglobulin levels, and various in vitro tests of cellular and humoral immune function; (2) total red blood cell deoxyadenosine nucleotides (dAXP) and, if on ERT, plasma ADA activity; and (3) screening for Epstein-Bar virus (EBV)-related lymphoma or other lymphomas after age three years, particularly when lymphocyte counts are declining while on prolonged ERT. Agents/circumstances to avoid: To ensure the safety of the infant/older individual with ADA deficiency while treatment to achieve immunocompetence is pending, parents and other care providers need to avoid the following risks of infection: (1) breastfeeding and breast milk until maternal CMV status is established by CMV serologies; (2) exposure to young children, sick contacts, individuals with cold sores, crowded enclosed spaces, and sources of aerosolized fungal spores such as areas of construction or soil manipulation; (3) live viral vaccines for the affected infant as well as household contacts; and (4) transfusion of non-irradiated blood products. Medications to avoid include adenine arabinoside, a substrate for ADA, as an antiviral agent and/or as chemotherapy of malignancies; and pentostatin, a potent ADA inhibitor used to treat some lymphoid malignancies, which would be ineffective in persons with ADA deficiency and would interfere with PEGylated ADA. Evaluation of relatives at risk: In an at-risk fetus, when the ADA pathogenic variants causing ADA-SCID in the family are known, prenatal genetic testing may be performed to help prepare for optimal management of an affected infant at birth (i.e., identification of a center with expertise in SCID treatment protocols that can help initiate ERT and the search for an HSCT donor and explain ways to ensure the safety of the infant while awaiting HSCT). If prenatal testing has not been performed, an at-risk newborn clinically suspected of SCID should immediately be placed in an appropriate environment to reduce the risk of infection, and the following testing should be performed before administration of a blood transfusion to allow earliest possible diagnosis and initiation of treatment: identification of the ADA pathogenic variants and measurement of ADA catalytic activity and level of dAXP in red blood cells.Therapies under investigation: Various approaches to HSC-GT are under investigation.ADA deficiency is inherited in an autosomal recessive manner. If both parents are known to be heterozygous for an ADA pathogenic variant, each sib of an affected individual has at conception a 25% chance of being affected, a 50% chance of being an asymptomatic carrier, and a 25% chance of inheriting neither of the familial pathogenic variants. An individual who inherits two pathogenic ADA variants will have either ADA-SCID or a delayed or late-onset ADA-CID phenotype that correlates with the least severe ADA pathogenic variant inherited. Once the ADA pathogenic variants have been identified in an affected family member, carrier testing for at-risk relatives and prenatal and preimplantation genetic testing are possible.Copyright © 1993-2025, University of Washington, Seattle. GeneReviews is a registered trademark of the University of Washington, Seattle. All rights reserved.

IPEX (immune dysregulation, polyendocrinopathy, enteropathy, X-linked) syndrome is characterized by systemic autoimmunity, typically beginning in the first year of life, which includes the triad of enteropathy (manifesting as malabsorption and watery diarrhea), endocrinopathy (most commonly type 1 insulin-dependent diabetes mellitus), and eczematous dermatitis. In addition to these manifestations, many children have other autoimmune phenomena including cytopenias, autoimmune hepatitis, nephropathy, lymphadenopathy, splenomegaly, alopecia, arthritis, and interstitial lung disease related to immune dysregulation. Fetal presentation of IPEX syndrome includes hydrops, echogenic bowel, skin desquamation, intrauterine growth deficiency, and fetal akinesia. Without aggressive immunosuppression or hematopoietic stem cell transplantation (HSCT), the majority of affected males will die within the first one to two years of life from metabolic derangements, severe malabsorption, or sepsis. Individuals with a milder phenotype have survived into the second or third decade of life, but this is uncommon.The diagnosis is established in a male proband with typical clinical findings, absent regulatory T cells (Treg) in blood or tissues, decreased numbers of FOXP3-expressing T cells in peripheral blood determined by flow cytometry (although FOXP3 levels in Treg can be normal in some individuals), and a hemizygous pathogenic variant in FOXP3 identified by molecular genetic testing. Heterozygous females have not been reported to have clinical findings typical of IPEX syndrome.Targeted therapies: HSCT offers the only potential cure for IPEX syndrome. T cell-directed immune suppression can include either an mTOR inhibitor (sirolimus) or calcineurin inhibitor (cyclosporin A or tacrolimus), alone or in combination with corticosteroids. Supportive care: Total parenteral nutrition (TPN) with fluids and electrolyte support is needed until intestinal function can be established with immune suppression. Treatment of type 1 insulin-dependent diabetes mellitus with insulin and carbohydrate management is standard, as is management of autoimmune thyroid disease. Skin conditions are managed with topical therapies, which can include steroids, tacrolimus, and emollients. Autoimmune neutropenia has been successfully treated with granulocyte colony-stimulating factor; pemphigus nodularis has been treated with rituximab (anti-CD20), and rituximab has been used for other autoantibody-mediated disease. Prophylactic antibiotic therapy may be required for autoimmune neutropenia or recurrent infections with central venous access and TPN. Aggressive management of dermatitis with topical steroids and anti-inflammatory agents as needed to prevent cutaneous infections. Surveillance: Monitor growth, nutritional intake, and stooling patterns at each visit; glucose tolerance test, hemoglobin A1c, and thyroid function tests every three to six months; skin exam at each visit; complete blood count, blood urea nitrogen, creatinine, urinalysis, and serum aspartate transaminase and alanine transaminase every three to six months. Agents/circumstances to avoid: Withhold immunizations until after HSCT, if possible. Evaluation of relatives at risk: It is appropriate to clarify the genetic status of at-risk males either prenatally or immediately after birth to enable early diagnosis and HSCT and/or immune suppression treatment in affected males before significant organ damage occurs.IPEX syndrome is inherited in an X-linked manner. The risk to sibs of the proband depends on the genetic status of the mother. If the mother of the proband has a FOXP3 pathogenic variant, the chance of transmitting the pathogenic variant in each pregnancy is 50%. Males who inherit the pathogenic variant will be affected; females who inherit the pathogenic variant will be heterozygous (to date, IPEX syndrome has not been reported in females who are heterozygous for a FOXP3 pathogenic variant). Affected males transmit the pathogenic variant to all of their daughters and none of their sons. Once the FOXP3 pathogenic variant has been identified in an affected family member, identification of female heterozygotes and prenatal/preimplantation genetic testing are possible.Copyright © 1993-2025, University of Washington, Seattle. GeneReviews is a registered trademark of the University of Washington, Seattle. All rights reserved.

Gaucher disease (GD) encompasses a continuum of clinical findings from a perinatal-lethal disorder to an asymptomatic type. The characterization of three major clinical types (1, 2, and 3) and two clinical forms (perinatal-lethal and cardiovascular) is useful in determining prognosis and management. Cardiopulmonary complications have been described with all the clinical phenotypes, although varying in frequency and severity. Type 1GD is characterized by the presence of clinical or radiographic evidence of bone disease (osteopenia, focal lytic or sclerotic lesions, and osteonecrosis), hepatosplenomegaly, anemia, thrombocytopenia, lung disease, and the absence of primary central nervous system disease. Type 2 GD is characterized by primary central nervous system disease with onset before age two years, limited psychomotor development, and a rapidly progressive course with death by age two to four years. Type 3 GD is characterized by primary central nervous system disease with childhood onset, a more slowly progressive course, and survival into the third or fourth decade. The perinatal-lethal form is associated with ichthyosiform or collodion skin abnormalities or with nonimmune hydrops fetalis. The cardiovascular form is characterized by calcification of the aortic and mitral valves, mild splenomegaly, corneal opacities, and supranuclear ophthalmoplegia.The diagnosis of GD relies on demonstration of deficient glucocerebrosidase (glucosylceramidase) enzyme activity in peripheral blood leukocytes or other nucleated cells, or by the identification of biallelic pathogenic variants in GBA1 on molecular genetic testing.Targeted therapy: Options include enzyme replacement therapy (ERT) or substrate reduction therapy (SRT; e.g., miglustat, eliglustat). Hematopoietic stem cell transplantation may be an option in individuals with severe GD, primarily those with chronic neurologic involvement (type 3 GD). Supportive care: When possible, management by a multidisciplinary team at a GD Comprehensive Treatment Center. Symptomatic treatment includes partial or total splenectomy for those with massive splenomegaly, significant areas of splenic fibrosis, and persistent significant thrombocytopenia (platelets <30,000/mm3) with a risk of bleeding; splenectomy may be needed even in those on targeted therapy. Supportive care for all affected individuals may include: orthopedic management of bone disease; analgesics for bone pain; joint replacement surgery for relief from chronic pain and restoration of function; anti-bone resorptive agents, calcium, and vitamin D for osteoporosis; transfusion of blood products for severe anemia and bleeding; the use of anticoagulants in individuals with severe thrombocytopenia and/or coagulopathy should be discussed with a hematologist to avoid the possibility of excessive bleeding; treatment of cholelithiasis, pulmonary disease, pulmonary hypertension, multiple myeloma, psychological manifestations, parkinsonism, and seizures according to the relevant specialist; social work support and care coordination as needed. Surveillance: Clinical assessment of disease progression at least every six months to include hematologic, orthopedic, pulmonary, cardiac, psychiatric, and neurologic assessment; clinical assessment for abdominal pain, early satiety, evidence of bleeding diathesis, growth and weight gain, clinical disease markers, and liver enzymes; imaging for spleen and liver volumes at least every one to two years. Additional evaluations to be done as needed include radiographs, MRI, and dual-energy x-ray absorptiometry (DXA) scan; bone age in children with growth and pubertal delay; ultrasound for gallstones; serum iron, ferritin, and vitamin B12 in those with anemia; and EKG and echocardiography with Doppler in individuals after splenectomy and those with elevated pulmonary artery pressure. Agents/circumstances to avoid: Nonsteroidal anti-inflammatory drugs in individuals with moderate-to-severe thrombocytopenia. Evaluation of relatives at risk: It is appropriate to offer testing to asymptomatic at-risk relatives so that those with glucocerebrosidase enzyme deficiency or biallelic pathogenic variants can benefit from early diagnosis and treatment if indicated. Pregnancy management: Pregnancy can exacerbate preexisting symptoms and trigger new features in affected women. Those with severe thrombocytopenia and/or clotting abnormalities are at increased risk for bleeding around the time of delivery. Evaluation by a hematologist prior to delivery is recommended. The lack of studies on the safety of eliglustat use during pregnancy and lactation has led to the recommendation that this medication be avoided during pregnancy, if possible.GD is inherited in an autosomal recessive manner. The parents of an affected individual are typically heterozygous for a GBA1 pathogenic variant; in some families, an asymptomatic parent may be found to be homozygous rather than heterozygous. If both parents are known to be heterozygous for a GBA1 pathogenic variant, each sib of an affected individual has at conception a 25% chance of being affected, a 50% chance of being a heterozygote, and a 25% chance of inheriting neither of the familial GBA1 pathogenic variants. Once the GBA1 pathogenic variants have been identified in an affected family member, molecular genetic carrier testing for at-risk family members, preimplantation genetic testing, and prenatal testing for GD are possible. The identification of 0%-15% of normal glucocerebrosidase enzyme activity in fetal samples obtained by chorionic villus sampling (CVS) or amniocentesis – ideally complemented by molecular genetic testing – can also be used to establish affected status in a fetus.Copyright © 1993-2025, University of Washington, Seattle. GeneReviews is a registered trademark of the University of Washington, Seattle. All rights reserved.

Single large-scale mitochondrial DNA deletion syndromes (SLSMDSs) comprise overlapping clinical phenotypes including Kearns-Sayre syndrome (KSS), KSS spectrum, Pearson syndrome (PS), chronic progressive external ophthalmoplegia (CPEO), and CPEO-plus. KSS is a progressive multisystem disorder with onset before age 20 years characterized by pigmentary retinopathy, CPEO, and cardiac conduction abnormality. Additional features can include cerebellar ataxia, tremor, intellectual disability or cognitive decline, dementia, sensorineural hearing loss, oropharyngeal and esophageal dysfunction, exercise intolerance, muscle weakness, and endocrinopathies. Brain imaging typically shows bilateral lesions in the globus pallidus and white matter. KSS spectrum includes individuals with KSS in addition to individuals with ptosis and/or ophthalmoparesis and at least one of the following: retinopathy, ataxia, cardiac conduction defects, hearing loss, growth deficiency, cognitive impairment, tremor, or cardiomyopathy. Compared to CPEO-plus, individuals with KSS spectrum have more severe muscle involvement (e.g., weakness, atrophy) and overall have a worse prognosis. PS is characterized by pancytopenia (typically transfusion-dependent sideroblastic anemia with variable cell line involvement), exocrine pancreatic dysfunction, poor weight gain, and lactic acidosis. PS manifestations also include renal tubular acidosis, short stature, and elevated liver enzymes. PS may be fatal in infancy due to neutropenia-related infection or refractory metabolic acidosis. CPEO is characterized by ptosis, ophthalmoplegia, oropharyngeal weakness, variable proximal limb weakness, and/or exercise intolerance. CPEO-plus includes CPEO with additional multisystemic involvement including neuropathy, diabetes mellitus, migraines, hypothyroidism, neuropsychiatric manifestations, and optic neuropathy. Rarely, an SLSMDS can manifest as Leigh syndrome, which is characterized as developmental delays, neurodevelopmental regression, lactic acidosis, and bilateral symmetric basal ganglia, brain stem, and/or midbrain lesions on MRI.The diagnosis of an SLSMDS is established in a proband with characteristic clinical features by identification of a mitochondrial DNA (mtDNA) deletion ranging in size from 1.1 to 10 kb on molecular genetic testing. SLSMDSs can be identified in DNA from blood, buccal cells, and urine in affected children; analysis of skeletal muscle tissue may be required to detect an SLSMDS in an affected adult.Targeted therapy: Folinic acid supplementation in individuals with KSS with low 5-methyltetrahydrofolate in CSF or white matter abnormalities on brain MRI. Supportive care: Consider mitochondrial supplement therapies such as coenzyme Q10 and antioxidants; optimize nutrition and exercise regimen to prevent acute decompensation; physical and occupational therapy for myopathy and/or ataxia; standard treatment with anti-seizure medication; hearing aids or cochlear implants for sensorineural hearing loss; developmental and educational support; feeding therapy; consider gastrostomy tube placement if poor weight gain, choking, or aspiration risk is present; dilation of the upper esophageal sphincter to alleviate cricopharyngeal achalasia; prophylactic placement of cardiac pacemaker in individuals with cardiac conduction block, with consideration of an implantable cardioverter defibrillator; hormone replacement therapy per endocrinologist; electrolyte monitoring and replacement for renal tubular acidosis; eyelid slings and/or ptosis repair for severe ptosis; eye ointment for dry eyes; eyeglass prisms for diplopia; transfusion therapy for individuals with PS with sideroblastic anemia; replacement of pancreatic enzymes for exocrine pancreatic insufficiency; ventilatory support for respiratory abnormalities that may occur in individuals with Leigh syndrome; standard treatment of anxiety and/or depression; social work support and care coordination as needed. Surveillance: Annual neurology assessment for ataxia, neuropathy, seizures, and myopathy; annual audiology evaluation; annual assessment of developmental progress, educational needs, and cognitive issues; annual evaluation by a neuro-ophthalmologist and/or retinal specialist and oculoplastics; measurement of growth parameters and evaluation of nutritional status and safety of oral intake at each visit; annual assessment of mobility and self-help skills with physical medicine, occupational therapy, and/or physical therapy; EKG and echocardiogram every six to 12 months; annual assessment with an endocrinologist; BUN and creatinine, with consideration of cystatin C in those with low muscle mass; complete blood count in those with PS to assess transfusion needs with additional labs per hematologist, and ferritin for those needing recurrent transfusions as needed; annual complete blood count in those with other SLSMDSs; fecal fat and fecal elastase as needed based on symptoms; monitor for evidence of aspiration and respiratory insufficiency at each visit; assess family needs at each visit. Agents/circumstances to avoid: Volatile anesthetic hypersensitivity may occur. Avoid prolonged treatment with propofol (>30-60 minutes). Medications should be reviewed with a physician familiar with mitochondrial disorders including a thorough individualized assessment of risk vs benefit as several medications may be toxic to mitochondria.SLSMDSs are almost never inherited, suggesting that these disorders are typically caused by a de novo single large-scale mitochondrial DNA deletion (SLSMD) that occurs in the mother's oocytes during germline development or in the embryo during embryogenesis. If the mother is clinically unaffected and the proband represents a simplex case (i.e., a single affected family member), the empiric risk to the sibs of a proband is very low (at or below 1%). If the mother is affected, the recurrence risk to sibs is estimated to be approximately 4% (one in 24 births). Maternal transmission to more than one child has not been reported to date. Prenatal testing for a pregnancy at increased risk and preimplantation genetic testing are scientifically possible but technically prohibitive as next-generation sequencing methodology does not accurately quantify heteroplasmy level of an SLSMD and droplet digital quantitative PCR cannot reliably detect less than 10% heteroplasmy levels of an SLSMD. Further, prenatal testing is not clinically available due to the inability to accurately interpret the clinical prognosis based on prenatal diagnostic results of an SLSMD.Copyright © 1993-2025, University of Washington, Seattle. GeneReviews is a registered trademark of the University of Washington, Seattle. All rights reserved.

Diamond-Blackfan anemia (DBA) is characterized by a profound normochromic and usually macrocytic anemia with normal leukocytes and platelets, congenital malformations in up to 50%, and growth deficiency in 30% of affected individuals. The hematologic complications occur in 90% of affected individuals during the first year of life. The phenotypic spectrum ranges from a mild form (e.g., mild anemia or no anemia with only subtle erythroid abnormalities, physical malformations without anemia) to a severe form of fetal anemia resulting in nonimmune hydrops fetalis. DBA is associated with an increased risk for acute myelogenous leukemia (AML), myelodysplastic syndrome (MDS), and solid tumors including osteogenic sarcoma.The clinical diagnosis can be established in a proband with macrocytic anemia with onset prior to age one year, no other significant cytopenias, reticulocytopenia, normal marrow cellularity with a paucity of erythroid precursors, and no evidence of another acquired or inherited disorder of bone marrow function. The molecular diagnosis can be established in a female proband by identification of a heterozygous pathogenic variant in one of the 22 genes associated with DBA. The molecular diagnosis can be established in a male proband by identification of a heterozygous pathogenic variant in a gene associated with autosomal dominant DBA or identification of a hemizygous pathogenic variant in GATA1 or TSR2 (associated with X-linked inheritance).Treatment of manifestations: Corticosteroid treatment, recommended in children older than age 12 months, improves the red blood cell count in approximately 80% of affected individuals. Chronic transfusion with packed red blood cells is necessary during the first year of life to avoid steroid-induced toxicity in those not responsive to a trial of corticosteroids at age 12 months and in individuals who relapse. Hematopoietic stem cell transplantation, the only curative therapy for the hematologic manifestations of DBA, is often recommended for those who are transfusion dependent or develop other cytopenias. Ocular, skeletal, genitourinary, cardiac, and endocrine complications are best managed in collaboration with appropriate subspecialists. Treatment of malignancies should be coordinated by an oncologist. Chemotherapy must be given cautiously as it may lead to prolonged cytopenia and subsequent toxicities. Prevention of secondary complications: Transfusion-related iron overload is the most common complication in transfusion-dependent individuals. Iron chelation therapy with deferasirox orally or desferrioxamine subcutaneously is recommended after ten to 12 transfusions. Corticosteroid-related side effects must also be closely monitored, especially as related to risk for infection, growth deficiency, and loss of bone density in growing children. Often individuals will be placed on transfusion therapy if these side effects are intolerable. Surveillance: Complete blood counts several times a year; bone marrow aspirate/biopsy to evaluate morphology and cellularity only in the event of another cytopenia or a change in response to treatment. In steroid-dependent individuals: monitor blood pressure and (in children) growth. Evaluation by an endocrinologist for those who are steroid dependent and those at risk for transfusion iron overload. Cancer surveillance includes history, physical examination, and blood counts every four to six months. If red blood cell, white blood cell, or platelet counts fall rapidly, bone marrow aspirate with biopsy and cytogenetic studies (including karyotype and FISH analysis) to look for acquired abnormalities in chromosomes 5, 7, and 8 that are associated with myelodysplastic syndrome or leukemia. Agents/circumstances to avoid: Deferiprone for the treatment of iron overload (which can cause neutropenia); infection (especially in individuals on corticosteroids). Evaluation of relatives at risk: Molecular genetic testing of at-risk relatives of a proband with a known pathogenic variant allows for early diagnosis and appropriate monitoring for bone marrow failure, physical abnormalities, and related cancers. Pregnancy management: Management by an obstetrician with expertise in high-risk pregnancies and hematologists with experience in bone marrow failure syndromes. During pregnancy the maternal hemoglobin level must be monitored. Use of low-dose aspirin up to 37 weeks' gestation may help prevent vasculo-placental complications in women with a history of a problematic pregnancy.DBA is most often inherited in an autosomal dominant manner; GATA1-related and TSR2-related DBA are inherited in an X-linked manner. Autosomal dominant. Approximately 40%-45% of individuals with autosomal dominant DBA have inherited the pathogenic variant from a parent; approximately 55%-60% have a de novo pathogenic variant. Each child of an individual with autosomal dominant DBA has a 50% chance of inheriting the pathogenic variant. X-linked. Males with GATA1- or TSR2-related DBA pass the pathogenic variant to all of their daughters and none of their sons. Women heterozygous for a GATA1 or TSR2 pathogenic variant have a 50% chance of transmitting the pathogenic variant in each pregnancy: males who inherit the pathogenic variant will be affected; females who inherit the pathogenic variant will be carriers and will usually not be affected. Carrier testing of at-risk female relatives is possible if the GATA1 or TSR2 pathogenic variant has been identified in the family. Once the DBA-causing pathogenic variant has been identified in an affected family member, prenatal testing for a pregnancy at increased risk and preimplantation genetic testing are possible.Copyright © 1993-2025, University of Washington, Seattle. GeneReviews is a registered trademark of the University of Washington, Seattle. All rights reserved.

ZAP70-related combined immunodeficiency (ZAP70-related CID) is a cell-mediated immunodeficiency caused by abnormal T-cell receptor (TCR) signaling. Affected children usually present in the first year of life with recurrent bacterial, viral, and opportunistic infections, diarrhea, and failure to thrive. Severe lower-respiratory infections and oral candidiasis are common. Affected children usually do not survive past their second year without hematopoietic stem cell transplantation (HSCT).The diagnosis of ZAP70-related CID is suggested by low to absent CD8+ T cells in an individual with normal CD3+ and CD4+ T-cell counts. Additional supportive laboratory features include absent proliferation of CD4+ T cells in response to mitogens and antigens, and absent ZAP-70 protein expression. The diagnosis is established in a proband by identification of biallelic pathogenic variants in ZAP70 on molecular genetic testing.Treatment of manifestations: Supportive care includes immediate intravenous immunoglobulin (IVIG) and antibacterial, antifungal, antiviral, and Pneumocystisjiroveci prophylaxis to control and reduce the occurrence of infections. Prevention of primary manifestations: Allogeneic HSCT to reconstitute the immune system, preferably prior to the onset of infections. Prevention of secondary complications: Use of irradiated, leukoreduced, cytomegalovirus (CMV)-safe blood products; deferment of immunizations until immune reconstitution; consideration for formula feeds in place of breast feeding until CMV status of mother is known. Surveillance: Individuals with milder findings or those who have not undergone HSCT need to be monitored for worsening of immune function with periodic assessment of clinical status and functional lymphocyte responsiveness. Following a successful HSCT, the following should be routinely monitored: growth, psychomotor development, complete blood counts, liver and renal function, immune status, donor and recipient chimerism, development of post-transplant complications. Agents/circumstances to avoid: Non-irradiated blood products; live viral, live mycobacterial, and live bacterial vaccinations; contaminated water sources; exposure to fungus-enriched environments (e.g., construction sites, agricultural areas with active soil disruption, mulch, hay). Evaluation of relatives at risk: Because the outcome of HSCT in children with ZAP70-related CID is significantly improved by performing HSCT prior to the onset of severe infections, early testing of at-risk sibs should be considered. In addition, any sibs considered as bone marrow donors must be evaluated for ZAP70-related CID prior to donation.ZAP70-related CID is inherited in an autosomal recessive manner. At conception, each sib of an affected individual has a 25% chance of being affected, a 50% chance of being a carrier, and a 25% chance of being unaffected and not a carrier. Carrier testing for at-risk family members and prenatal diagnosis for pregnancies at increased risk are possible if the pathogenic variants in the family are known.Copyright © 1993-2025, University of Washington, Seattle. GeneReviews is a registered trademark of the University of Washington, Seattle. All rights reserved.

Fanconi anemia (FA) is characterized by physical abnormalities, bone marrow failure, and increased risk for malignancy. Physical abnormalities, present in approximately 75% of affected individuals, include one or more of the following: short stature, abnormal skin pigmentation, skeletal malformations of the upper and/or lower limbs, microcephaly, and ophthalmic and genitourinary tract anomalies. Progressive bone marrow failure with pancytopenia typically presents in the first decade, often initially with thrombocytopenia or leukopenia. The incidence of acute myeloid leukemia is 13% by age 50 years. Solid tumors – particularly of the head and neck, skin, and genitourinary tract – are more common in individuals with FA.The diagnosis of FA is established in a proband with increased chromosome breakage and radial forms on cytogenetic testing of lymphocytes with diepoxybutane (DEB) and mitomycin C (MMC) and/or one of the following identified on molecular genetic testing: biallelic pathogenic variants in one of the 21 genes known to cause autosomal recessive FA; a heterozygous pathogenic variant in RAD51 known to cause autosomal dominant FA; or a hemizygous pathogenic variant in FANCB known to cause X-linked FA.Treatment of manifestations: Administration of oral androgens (e.g., oxymetholone) improves blood counts (red cell and platelets) in approximately 50% of individuals with FA; granulocyte colony-stimulating factor improves the neutrophil count in some individuals; hematopoietic stem cell transplantation (HSCT) is the only curative therapy for the hematologic manifestations of FA, but the high risk for solid tumors remains and may even be increased in those undergoing HSCT. All these treatments have potential significant toxicity. early detection and surgical removal remains the mainstay of therapy for solid tumors. Treatment of growth deficiency, limb anomalies, ocular anomalies, renal malformations, genital anomalies, hypothyroidism, cardiac anomalies, and dermatologic manifestations as recommended by the subspecialty care provider. Hearing aids may be helpful for hearing loss as per otolaryngologist; supplemental feeding as needed by nasogastric tube or gastrostomy; vitamin D supplementation; early intervention for developmental delays; individualized education plan for school-age children; speech, occupational, and physical therapy as needed; liberal use of sunscreen and rash guards; social work and care coordination as needed. Prevention of primary manifestations: Human papilloma virus (HPV) vaccination to reduce the risk for gynecologic cancer in females, and possibly reduce the risk of oral cancer in all individuals. Prevention of secondary complications: T-cell depletion of the donor graft to minimize the risk of graft-vs-host disease; conditioning regimen without radiation prior to HSCT to reduce the subsequent risk of developing solid tumors. Surveillance: Clinical assessment of growth, feeding, nutrition, spine, and ocular issues at each visit throughout childhood. Annual ophthalmology examination; annual evaluation with endocrinologist including TSH, free T4, 25-hydroxy vitamin D, two-hour glucose tolerance testing, and insulin levels; assessment of pubertal stage and hormone levels at puberty and every two years until puberty is complete; follow up hearing evaluation if exposed to ototoxic drugs; annual developmental assessment; blood counts every three to four months or as needed; bone marrow aspirate and biopsy to evaluate morphology and cellularity, FISH and cytogenetics to evaluate for emergence of a malignant clone at least annually after age two years; liver function tests every three to six months and liver ultrasound examination every six to twelve months in those receiving androgen therapy; gynecologic assessment for genital lesions annually beginning at age 13 years; vulvo-vaginal examinations and Pap smear annually beginning at age 18 years; oral examinations for tumors every six months beginning at age nine to ten years; annual nasolaryngoscopy beginning at age ten years; dermatology evaluation every six to 12 months; annual abdominal ultrasound and brain MRI in those with BRCA2-related FA. Additional cancer surveillance for individuals with BRCA1-, BRCA2-, PALB2-, BRIP1-, and RAD51C-related FA. Agents/circumstances to avoid: Transfusions of red cells or platelets for persons who are candidates for HSCT; family members as blood donors if HSCT is being considered; blood products that are not filtered (leukodepleted) or irradiated; toxic agents that have been implicated in tumorigenesis; unsafe sex practices, which increase the risk of HPV-associated malignancy; excessive sun exposure. Radiographic studies solely for the purpose of surveillance (i.e., in the absence of clinical indications) should be minimized. Evaluation of relatives at risk: DEB/MMC testing or molecular genetic testing (if the family-specific pathogenic variants are known) of all sibs of a proband for early diagnosis, treatment, and monitoring for physical abnormalities, bone marrow failure, and related cancers.Fanconi anemia (FA) can be inherited in an autosomal recessive manner, an autosomal dominant manner (RAD51-related FA), or an X-linked manner (FANCB-related FA). Autosomal recessive FA: Each sib of an affected individual has a 25% chance of inheriting both pathogenic variants and being affected, a 50% chance of inheriting one pathogenic variant and being a heterozygote, and a 25% chance of inheriting neither of the familial FA-related pathogenic variants. Heterozygotes are not at risk for autosomal recessive FA. However, heterozygous mutation of a subset of FA-related genes (e.g., BRCA1, BRCA2, PALB2, BRIP1, and RAD51C) is associated with an increased risk for breast and other cancers. Autosomal dominant FA: Given that all affected individuals with RAD51-related FA reported to date have the disorder as a result of a de novo RAD51 pathogenic variant, the risk to other family members is presumed to be low. X-linked FA: For carrier females the chance of transmitting the pathogenic variant in each pregnancy is 50%; males who inherit the pathogenic variant will be affected; females who inherit the pathogenic variant will be carriers and will usually not be affected. Carrier testing for at-risk relatives (for autosomal recessive and X-linked FA) and prenatal and preimplantation genetic testing are possible if the pathogenic variant(s) in the family are known.Copyright © 1993-2025, University of Washington, Seattle. GeneReviews is a registered trademark of the University of Washington, Seattle. All rights reserved.

Culture systems for human pluripotent stem cell (hPSC) expansion help enable the generation of a nearly unlimited pool of cells for use in downstream differentiation, disease modeling, drug discovery, and therapeutic applications. Monolayer culture is desirable in many circumstances due to the long history of validated assays and differentiation protocols. General culture protocols typically focus on methods for small plate formats (e.g., 6-well plate) yielding approximately 20 million hPSCs per plate. However, for some high-throughput screening and therapeutic applications, hPSCs expanded to a scale exceeding 1 billion cells may be required. This chapter provides a method for scale-out of hPSCs in monolayer cell culture conditions using commercially available cell culture media systems in conjunction with large surface area vessels. This scale-out procedure uses cell therapy grade reagents, which make application of cells and cell products to patients possible. It also provides insight into how to monitor cell health, assess pluripotency in normal stem cell cultures, and evaluates the capability to cryopreserve high cell densities.

CEBPA-associated familial acute myeloid leukemia (AML) is defined as the presence of a heterozygous germline CEBPA pathogenic variant in an individual with AML and/or family in which more than one individual has AML. In contrast, sporadic CEBPA-associated AML is defined as AML in which a CEBPA pathogenic variant(s) is identified in leukemic cells but not in the non-leukemic cells. In the majority of individuals, the age of onset of familial AML appears to be earlier than sporadic AML; disease onset has been reported in persons as young as age 1.8 years and up to age 50 years. The prognosis of CEBPA-associated familial AML appears to be favorable compared with sporadic CEBPA-associated AML. Individuals with CEBPA-associated familial AML who have been cured of their initial disease may be at greater risk of developing additional independent leukemic episodes, in addition to the risk of relapse from preexisting clones.The diagnosis of CEBPA-associated familial AML is established by identification of a heterozygous germline CEBPA pathogenic variant in a specimen that contains only non-leukemic cells from an individual and/or family with AML.Treatment of manifestations: Treatment usually includes cytarabine/anthracycline-based induction and cytarabine-based consolidation chemotherapy. Hematopoietic stem cell transplantation (HSCT) from a volunteer unrelated donor or appropriately screened family member should be reserved for individuals failing to achieve remission following standard induction therapy or for disease recurrence. Whenever possible, persons with AML should be treated as part of a clinical trial protocol. Surveillance: Similar to that for other forms of AML; because of the increased risk of late leukemia recurrence in persons with familial AML, lifelong surveillance is recommended. Asymptomatic individuals should have a CBC every six to 12 months and bone marrow examination for CBC abnormalities. Agents/circumstances to avoid: Use of sib or related donors for HSCT without prior assessment of the germline CEBPA pathogenic variant in the donor.Predisposition to CEBPA-associated familial AML is inherited in an autosomal dominant manner. Most individuals diagnosed with CEBPA-associated familial AML have had an affected parent who shares the germline pathogenic variant. Germline CEBPA pathogenic variants exhibit complete or near-complete penetrance for the development of AML in families reported to date. Each child of an affected individual has a 50% chance of inheriting the germline pathogenic variant. Prenatal testing for pregnancies at increased risk is possible if the germline CEBPA pathogenic variant in the family is known.Copyright © 1993-2025, University of Washington, Seattle. GeneReviews is a registered trademark of the University of Washington, Seattle. All rights reserved.

Myelosuppression is a common dose limiting toxicity of cytotoxic oncology drugs. Nanoparticles may distribute to bone marrow and/or release drug that is delivered to bone marrow. Therefore, understanding potential toxicity of nanoparticles or drugs which nanoparticles carry is an important step in preclinical safety evaluation. Hematopoietic stem cells of bone marrow (BM) proliferate and differentiate to form discrete cell clusters or colonies. This document describes a protocol for quantitative analysis of granulocyte-macrophage (GM) colony-forming units (CFU), employing murine BM. This protocol can be used for both in vitro and ex vivo analyses. The in vitro protocol involves isolation of bone marrow cells from healthy animals, followed by treatment in vitro with nanoparticle formulations. In the ex vivo version, the bone marrow is isolated from animals injected with the nanoparticle formulation. The in vitro protocol does not account for nanoparticle biodistribution; however, in cases when dose information is not available and nanoparticle formulation is in the early phase of development, the in vitro protocol allows for rapid screening of potentially toxic nanoparticle formulations. The in vitro protocol can also give a quick estimation of the myelosuppressive potential of a cytotoxic oncology drug bound to a nanoparticle surface in comparison to a traditional formulation of the same cytotoxic oncology drug (for an example, see Figure 1).

X-linked hyper IgM syndrome (HIGM1), a disorder of abnormal T- and B-cell function, is characterized by low serum concentrations of IgG, IgA, and IgE with normal or elevated serum concentrations of IgM. Mitogen proliferation may be normal, but NK- and T-cell cytotoxicity can be impaired. Antigen-specific responses are usually decreased or absent. Total numbers of B cells are normal but there is a marked reduction of class-switched memory B cells. Defective oxidative burst of both neutrophils and macrophages has been reported. The range of clinical findings varies, even within the same family. More than 50% of males with HIGM1 develop symptoms by age one year, and more than 90% are symptomatic by age four years. HIGM1 usually presents in infancy with recurrent upper- and lower-respiratory tract bacterial infections, opportunistic infections including Pneumocystis jirovecii pneumonia, and recurrent or protracted diarrhea that can be infectious or noninfectious and is associated with failure to thrive. Neutropenia is common; thrombocytopenia and anemia are less commonly seen. Autoimmune and/or inflammatory disorders (such as sclerosing cholangitis) as well as increased risk for neoplasms have been reported as medical complications of this disorder. Significant neurologic complications, often the result of a CNS infection, are seen in 5%-15% of affected males. Liver disease, a serious complication of HIGM1 once observed in more than 80% of affected males by age 20 years, may be decreasing with adequate screening and treatment of Cryptosporidium infection.The diagnosis of X-linked hyper IgM syndrome is established in a male proband with typical clinical and laboratory findings and a hemizygous pathogenic variant in CD40LG identified by molecular genetic testing.Treatment of manifestations: Hematopoietic stem cell transplantation (HSCT) (the only curative treatment currently available), ideally performed before age ten years, prior to evidence of organ damage; immunoglobulin replacement therapy (either intravenous or subcutaneous); appropriate antimicrobial therapy for acute infections; antimicrobial prophylaxis for opportunistic infection against Pneumocysitis jirovecii pneumonia; recombinant granulocyte colony-stimulating factor for chronic neutropenia; immunosuppressants for autoimmune disorders. Agents/circumstances to avoid: Areas that place individual at risk of contracting Cryptosporidium including pools, lakes, ponds, or certain water sources; drinking unpurified or unfiltered water; live vaccines such as rotavirus, MMR, varicella, live attenuated polio, and BCG. Surveillance: At least annually: CBC with differential to monitor for cytopenias, testing of IgG levels and lymphocyte subpopulations, pulmonary function tests after age seven years. Regular assessment of liver function, consider abdominal imaging; as well as polymerase chain reaction-based testing for the presence of enteric pathogens including Cryptosporidium. Monitor growth and general health with a low threshold for lymph node biopsy, given elevated oncologic risk. Evaluation of relatives at risk: It is appropriate to clarify the genetic status of newborn at-risk relatives of an affected individual in order to identify as early as possible those who would benefit from early diagnosis and prompt initiation of treatment and prevention of infections.By definition, X-linked hyper IgM syndrome (HIGM1) is inherited in an X-linked manner. Affected males transmit the pathogenic variant to all their daughters and none of their sons. Women with a CD40LG pathogenic variant have a 50% chance of transmitting the pathogenic variant in each pregnancy. Males who inherit the pathogenic variant will be affected. Female who inherit the pathogenic variant will typically be asymptomatic but may have a range of clinical manifestation depending on X-chromosome inactivation. Once the CD40LG pathogenic variant has been identified in an affected family member, heterozygote testing for at-risk female relatives, prenatal testing for a pregnancy at increased risk, and preimplantation genetic testing for HIGM1 are possible.Copyright © 1993-2025, University of Washington, Seattle. GeneReviews is a registered trademark of the University of Washington, Seattle. All rights reserved.

Plerixafor is a small molecular antagonist of the cell-surface CXCR4 receptor that plays an important role in mobilization of hematopoietic stem and progenitor cells to the stroma of the bone marrow; blocking the receptor helps to mobilize stem cells from the marrow to peripheral blood allowing for collection of these cells by apheresis for hematopoietic cell transplantation. Plerixafor is generally well tolerated and has not been linked to serum enzyme elevations or to clinically apparent liver injury.