Classic ataxia-telangiectasia (A-T) is characterized by progressive cerebellar ataxia beginning between ages one and four years, oculomotor apraxia, choreoathetosis, telangiectasias of the conjunctivae, immunodeficiency, frequent infections, and an increased risk for malignancy, particularly leukemia and lymphoma. Individuals with A-T are unusually sensitive to ionizing radiation. Non-classic forms of A-T have included adult-onset A-T and A-T with early-onset dystonia.

Complement hyperactivation, angiopathic thrombosis, and protein-losing enteropathy (CHAPLE) is characterized by abdominal pain and diarrhea, primary intestinal lymphangiectasia, hypoproteinemic edema, and malabsorption. Some patients also exhibit bowel inflammation, recurrent infections associated with hypogammaglobulinemia, and/or angiopathic thromboembolic disease. Patient T lymphocytes show increased complement activation, causing surface deposition of complement and generating soluble C5a (Ozen et al., 2017).

The WAS-related disorders, which include Wiskott-Aldrich syndrome, X-linked thrombocytopenia (XLT), and X-linked congenital neutropenia (XLN), are a spectrum of disorders of hematopoietic cells, with predominant defects of platelets and lymphocytes caused by pathogenic variants in WAS. WAS-related disorders usually present in infancy. Affected males have thrombocytopenia with intermittent mucosal bleeding, bloody diarrhea, and intermittent or chronic petechiae and purpura; eczema; and recurrent bacterial and viral infections, particularly of the ear. At least 40% of those who survive the early complications develop one or more autoimmune conditions including hemolytic anemia, immune thrombocytopenic purpura, immune-mediated neutropenia, rheumatoid arthritis, vasculitis, 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 thrombocytopenia with small platelets; other complications of Wiskott-Aldrich syndrome, including eczema and immune dysfunction, are usually mild or absent. Males with XLN have congenital neutropenia, myeloid dysplasia, and lymphoid cell abnormalities.

A syndrome characterized by pancytopenia, immune deficiency and cutaneous malignancies.

X-linked agammaglobulinemia (XLA) is characterized by recurrent bacterial infections in affected males in the first two years of life. Recurrent otitis is the most common infection prior to diagnosis. Conjunctivitis, sinopulmonary infections, diarrhea, and skin infections are also frequently seen. Approximately 60% of individuals with XLA are recognized as having immunodeficiency when they develop a severe, life-threatening infection such as pneumonia, empyema, meningitis, sepsis, cellulitis, or septic arthritis. S pneumoniae and H influenzae are the most common organisms found prior to diagnosis and may continue to cause sinusitis and otitis after diagnosis and the initiation of gammaglobulin substitution therapy. Severe, difficult-to-treat enteroviral infections (often manifest as dermatomyositis or chronic meningoencephalitis) can be prevented by this treatment. The prognosis for individuals with XLA has improved markedly in the last 25 years as a result of earlier diagnosis, the development of preparations of gammaglobulin that allow normal concentrations of serum IgG to be achieved, and more liberal use of antibiotics.

Purine nucleoside phosphorylase deficiency is a rare autosomal recessive immunodeficiency disorder characterized mainly by decreased T-cell function. Some patients also have neurologic impairment (review by Aust et al., 1992).

Classic Ehlers-Danlos syndrome (cEDS) is a connective tissue disorder characterized by skin hyperextensibility, atrophic scarring, and generalized joint hypermobility (GJH). The skin is soft and doughy to the touch, and hyperextensible, extending easily and snapping back after release (unlike lax, redundant skin, as in cutis laxa). The skin is fragile, as manifested by splitting of the dermis following relatively minor trauma, especially over pressure points (knees, elbows) and areas prone to trauma (shins, forehead, chin). Wound healing is poor, and stretching of scars after apparently successful primary wound healing is characteristic. Complications of joint hypermobility, such as dislocations of the shoulder, patella, digits, hip, radius, and clavicle, usually resolve spontaneously or are easily managed by the affected individual. Other features include hypotonia with delayed motor development, fatigue and muscle cramps, and easy bruising. Mitral valve prolapse can occur infrequently, but tends to be of little clinical consequence. Aortic root dilatation has been reported, appears to be more common in young individuals, and rarely progresses.

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.

Collagen VI-related dystrophies (COL6-RDs) represent a continuum of overlapping clinical phenotypes with Bethlem muscular dystrophy at the milder end, Ullrich congenital muscular dystrophy (UCMD) at the more severe end, and a phenotype in between UCMD and Bethlem muscular dystrophy, referred to as intermediate COL6-RD. Bethlem muscular dystrophy is characterized by a combination of proximal muscle weakness and joint contractures. Hypotonia and delayed motor milestones occur in early childhood; mild hypotonia and weakness may be present congenitally. By adulthood, there is evidence of proximal weakness and contractures of the elbows, Achilles tendons, and long finger flexors. The progression of weakness is slow, and more than two thirds of affected individuals older than age 50 years remain independently ambulatory indoors, while relying on supportive means for mobility outdoors. Respiratory involvement is not a consistent feature. UCMD is characterized by congenital weakness, hypotonia, proximal joint contractures, and striking hyperlaxity of distal joints. Decreased fetal movements are frequently reported. Some affected children acquire the ability to walk independently; however, progression of the disease results in a loss of ambulation by age ten to eleven years. Early and severe respiratory insufficiency occurs in all individuals, resulting in the need for nocturnal noninvasive ventilation (NIV) in the form of bilevel positive airway pressure (BiPAP) by age 11 years. Intermediate COL6-RD is characterized by independent ambulation past age 11 years and respiratory insufficiency that is later in onset than in UCMD and results in the need for NIV in the form of BiPAP by the late teens to early 20s. In contrast to individuals with Bethlem muscular dystrophy, those with intermediate COL6-RD typically do not achieve the ability to run, jump, or climb stairs without use of a railing.

Geroderma osteodysplasticum (GO) is an autosomal recessive disorder characterized by skin wrinkling limited to the dorsa of hands and feet and to the abdomen, bowed long bones, and osteopenia with frequent fractures. There is a distinctive facial appearance with droopy skin at the cheeks, maxillary hypoplasia, and large ears. Adult patients appear prematurely aged (summary by Rajab et al., 2008).

Mulibrey nanism (MUL) is a rare autosomal recessive growth disorder with prenatal onset, including occasional progressive cardiomyopathy, characteristic facial features, failure of sexual maturation, insulin resistance with type 2 diabetes, and an increased risk for Wilms tumor (summary by Hamalainen et al., 2006).

Analbuminemia (ANALBA) is a rare autosomal recessive disorder manifested by the presence of a very low amount of circulating serum albumin. Affected individuals have few clinical symptoms other than mild edema, hypotension, fatigue, and occasionally a peculiar lower body lipodystrophy (mainly in adult females). The most common biochemical finding is a gross hyperlipidemia, with a significant increase in the total and LDL cholesterol concentrations, but normal concentrations of HDL cholesterol and triglycerides. Analbuminemia often leads to fetal or neonatal death in sibs in families of analbuminemic individuals, which may explain the rarity of the trait (summary by Caridi et al., 2014).

JAK3-deficient severe combined immunodeficiency (SCID) is an inherited disorder of the immune system. Individuals with JAK3-deficient SCID lack the necessary immune cells to fight off certain bacteria, viruses, and fungi. They are prone to repeated and persistent infections that can be very serious or life-threatening. Often the organisms that cause infection in people with JAK3-deficient SCID are described as opportunistic because they ordinarily do not cause illness in healthy people. Affected infants typically develop chronic diarrhea, a fungal infection in the mouth called oral thrush, pneumonia, and skin rashes. Persistent illness also causes affected individuals to grow more slowly than other children. Without treatment, people with JAK3-deficient SCID usually live only into early childhood.

Simpson-Golabi-Behmel syndrome type 2 (SGBS2) is an X-linked recessive disorder in which affected males have severely impaired intellectual development, ciliary dyskinesia, and macrocephaly (summary by Budny et al., 2006). For a general phenotypic description and a discussion of genetic heterogeneity of Simpson-Golabi-Behmel syndrome, see 312870.

Immunodeficiency-59 and hypoglycemia (IMD59) is an autosomal recessive primary immunologic disorder characterized by combined immunodeficiency and recurrent septic infections of the respiratory tract, skin, and mucous membranes, as well as disturbed glucose metabolism. Granulocytopenia and B-cell and dendritic cell deficiency are present (Haapaniemi et al., 2017).

Campomelic dysplasia (CD) is a skeletal dysplasia characterized by distinctive facies, Pierre Robin sequence with cleft palate, shortening and bowing of long bones, and clubfeet. Other findings include laryngotracheomalacia with respiratory compromise and ambiguous genitalia or normal female external genitalia in most individuals with a 46,XY karyotype. Many affected infants die in the neonatal period; additional findings identified in long-term survivors include short stature, cervical spine instability with cord compression, progressive scoliosis, and hearing impairment.

FRA12A is a folate-sensitive chromosomal fragile site prone to breakage. No consistent phenotype has been observed with FRA12A, and it can be inherited without phenotypic effect (Berg et al., 2000). However, impaired intellectual development with or without other anomalies has been described in patients with over 40% of cells expressing FRA12A (Winnepenninckx et al., 2007).

Congenital disorders of glycosylation (CDGs) are a genetically heterogeneous group of autosomal recessive disorders caused by enzymatic defects in the synthesis and processing of asparagine (N)-linked glycans or oligosaccharides on glycoproteins. Type I CDGs comprise defects in the assembly of the dolichol lipid-linked oligosaccharide (LLO) chain and its transfer to the nascent protein. These disorders can be identified by a characteristic abnormal isoelectric focusing profile of plasma transferrin (Leroy, 2006). For a discussion of the classification of CDGs, see CDG1A (212065).

G6PC3 deficiency is characterized by severe congenital neutropenia which occurs in a phenotypic continuum that includes the following: Isolated severe congenital neutropenia (nonsyndromic). Classic G6PC3 deficiency (severe congenital neutropenia plus cardiovascular and/or urogenital abnormalities). Severe G6PC3 deficiency (classic G6PC3 deficiency plus involvement of non-myeloid hematopoietic cell lines, additional extra-hematologic features, and pulmonary hypertension; known as Dursun syndrome). Neutropenia usually presents with recurrent bacterial infections in the first few months of life. Intrauterine growth restriction (IUGR), failure to thrive (FTT), and poor postnatal growth are common. Other findings in classic and severe G6PC3 deficiency can include inflammatory bowel disease (IBD) resembling Crohn's disease, and endocrine disorders (growth hormone deficiency, hypogonadotropic hypogonadism, and delayed puberty).

A rare autosomal recessive primary immunodeficiency characterized by absence of HLA class II molecules on the surface of immune cells, leading to severely impaired cellular and humoral immune response to foreign antigens, severe CD4+ T-cell lymphopenia, and hypogammaglobulinemia. The disease clinically manifests with early onset of severe and recurrent infections mainly of the respiratory and gastrointestinal tract, protracted diarrhea with failure to thrive, and autoimmune disease, and is frequently fatal in childhood.

Any autosomal agammaglobulinemia in which the cause of the disease is a mutation in the CD79A gene.

Individuals with ficolin-3 deficiency have highly variable manifestations and a variable age of symptom onset. Some patients may show increased susceptibility to infection in the perinatal or neonatal period, whereas others may show autoimmune features as adults. Ficolin-3, also known as H-ficolin, can activate the lectin pathway of the complement system; deficiency may thus lead to defects in the complement system (summary by Munthe-Fog et al., 2009 and Michalski et al., 2015). For a discussion of genetic heterogeneity of lectin complement activation pathway defects, see LCAPD1 (614372).

Immunodeficiency-110 (IMD110) is an autosomal recessive primary T-cell immunodeficiency syndrome characterized by progressive loss of naive T cells, recurrent bacterial, viral, and fungal infections, warts, and abscesses, and autoimmune manifestations. Patients are at risk for developing lymphoproliferative disorders or lymphoma, particularly associated with EBV. Some patients may show cardiac malformations, including atrial septal defect (Abdollahpour et al., 2012; Nehme et al., 2012).

FILS syndrome is characterized by mild facial dysmorphism, mainly malar hypoplasia, livedo on the skin since birth, immunodeficiency resulting in recurrent infections, and short stature (summary by Pachlopnik Schmid et al., 2012).

Immunodeficiency-8 with lymphoproliferation (IMD8) is an autosomal recessive primary immunodeficiency characterized by early-childhood onset of recurrent infections and lymphoproliferative disorders, often associated with EBV infection. Laboratory studies show defects in the numbers and function of certain lymphocyte subsets, particularly T cells (Moshous et al., 2013; Stray-Pedersen et al., 2014).

Combined immunodeficiency due to MALT1 deficiency is a rare, genetic form of primary immunodeficiency characterized by growth retardation, early recurrent pulmonary infections leading to bronchiectasis, inflammatory gastrointestinal disease, and other symptoms, such as rash, dermatitis, skin infections.

Autoimmune lymphoproliferative syndrome type III is an autosomal recessive disorder of immune dysregulation. The phenotype is variable, but most patients have significant lymphadenopathy associated with variable autoimmune manifestations. Some patients may have recurrent infections. Lymphocyte accumulation results from a combination of impaired apoptosis and excessive proliferation (summary by Oliveira, 2013). For a general description and a discussion of genetic heterogeneity of ALPS, see 601859.

Most characteristically, Aicardi-Goutières syndrome (AGS) manifests as an early-onset encephalopathy that usually, but not always, results in severe intellectual and physical disability. A subgroup of infants with AGS present at birth with abnormal neurologic findings, hepatosplenomegaly, elevated liver enzymes, and thrombocytopenia, a picture highly suggestive of congenital infection. Otherwise, most affected infants present at variable times after the first few weeks of life, frequently after a period of apparently normal development. Typically, they demonstrate the subacute onset of a severe encephalopathy characterized by extreme irritability, intermittent sterile pyrexias, loss of skills, and slowing of head growth. Over time, as many as 40% develop chilblain skin lesions on the fingers, toes, and ears. It is becoming apparent that atypical, sometimes milder, cases of AGS exist, and thus the true extent of the phenotype associated with pathogenic variants in the AGS-related genes is not yet known.

Immunodeficiency-22 (IMD22) is an autosomal recessive disorder characterized by the onset of recurrent bacterial, viral, and fungal respiratory, gastrointestinal, and skin infections in infancy or early childhood. Immunologic workup shows severe T-cell lymphopenia, particularly affecting the CD4+ subset, and impaired proximal TCR intracellular signaling and activation. Although NK cells and B cells are normal, some patients may have hypogammaglobulinemia secondary to the T-cell defect. There are variable manifestations, likely due to the severity of the particular LCK mutation: patients may develop prominent skin lesions resembling epidermodysplasia verruciformis, gastrointestinal inflammation, and virus-induced malignancy. The disease can be fatal in childhood, but hematopoietic stem cell transplant (HSCT) may be curative (Hauck et al., 2012; Li et al., 2016; Keller et al., 2023).

Infantile-onset multisystem autoimmune disease-1 is characterized by early childhood onset of a spectrum of autoimmune disorders affecting multiple organs. Common manifestations include insulin-dependent diabetes mellitus and autoimmune enteropathy, or celiac disease, and autoimmune hematologic disorders. Other features include short stature and nonspecific dermatitis. More variable features include hypothyroidism, autoimmune arthritis, and delayed puberty. Some patients may show recurrent infections. The disorder results from an inborn error of cytokine signaling (summary by Flanagan et al., 2014 and Milner et al., 2015). Genetic Heterogeneity of Infantile-Onset Multisystem Autoimmune Disease See also ADMIO2 (617006), caused by mutation in the ZAP70 gene (176947) on chromosome 2q12, and ADMIO3 (620430), caused by mutation in the CBLB gene (604491) on chromosome 3q13.

Severe combined immunodeficiency (SCID) due to DNA-PKcs deficiency is an extremely rare type of SCID (see this term) characterized by the classical signs of SCID (severe and recurrent infections, diarrhea, failure to thrive), absence of T and B lymphocytes, and cell sensitivity to ionizing radiation.

Immunodeficiency-36 with lymphoproliferation (IMD36) is an autosomal dominant primary immunodeficiency with a highly heterogeneous clinical phenotype, characterized primarily by recurrent respiratory tract infections, lymphoproliferation, and antibody deficiency. Other features include growth retardation, mild neurodevelopmental delay, and autoimmunity. The major complication is development of B-cell lymphoma (Elkaim et al., 2016).

Immune dysregulation with autoimmunity, immunodeficiency, and lymphoproliferation (IDAIL) is an autosomal dominant complex immune disorder with highly variable presentation and clinical manifestations. Prominent features include recurrent infections often associated with hypogammaglobulinemia, autoimmune features such as autoimmune cytopenias, and abnormal lymphocytic infiltration of nonlymphoid organs, including the lungs, brain, and gastrointestinal tract, resulting in enteropathy. Laboratory studies often show lymphopenia and abnormal T and B cell subsets. The variable features are a result of impaired function of Treg cells, which play a role in immune homeostasis (summary by Kuehn et al., 2014; Schwab et al., 2018, and Lopez-Nevado et al., 2021). The disorder shows overlapping features with autoimmune lymphoproliferative syndrome (ALPS); for a general description and a discussion of genetic heterogeneity of ALPS, see 601859.

Primary ciliary dyskinesia-33 is an autosomal recessive disorder characterized by recurrent upper and lower respiratory infections due to defective ciliary clearance and resulting in chronic lung disease. Some patients may have recurrent ear infections resulting in conductive hearing impairment. Examination of respiratory cilia shows subtle movement defects. Laterality defects have not been reported (summary by Olbrich et al., 2015). For a phenotypic description and a discussion of genetic heterogeneity of primary ciliary dyskinesia, see CILD1 (244400).

Congenital myasthenic syndrome-19 (CMS19) is an autosomal recessive disorder resulting from a defect in the neuromuscular junction, causing generalized muscle weakness, exercise intolerance, and respiratory insufficiency. Patients present with hypotonia, feeding difficulties, and respiratory problems soon after birth, but the severity of the weakness and disease course is variable (summary by Logan et al., 2015). For a discussion of genetic heterogeneity of CMS, see CMS1A (601462).

Myofibrillar myopathy-8 (MFM8) is an autosomal recessive myopathy characterized by slowly progressive proximal muscle weakness and atrophy affecting the upper and lower limbs, resulting in increased falls, gait problems, difficulty running or climbing stairs, and upper limb weakness or scapular winging. Some patients develop distal muscle weakness and atrophy. The phenotype may also be consistent with a clinical diagnosis of limb-girdle muscular dystrophy (LGMD). Age at symptom onset ranges from infancy to adulthood. Ambulation is generally preserved and cardiac involvement is rare, but respiratory compromise with decreased forced vital capacity often occurs. Muscle biopsy shows a mix of myopathic features, including myofibrillar inclusions and sarcomeric disorganization; some patients have been reported to have dystrophic changes on muscle biopsy (O'Grady et al., 2016; Daimaguler et al., 2021). There is significant phenotypic variation, even in patients with the same mutation, which must be taken into account when counseling affecting individuals (Woods et al., 2020). For a general phenotypic description and a discussion of genetic heterogeneity of myofibrillar myopathy, see MFM1 (601419).

IMDDHH is a multisystem disorder characterized by immunodeficiency, mildly delayed psychomotor development, poor overall growth from infancy, and hypohomocysteinemia. Additional features, such as congenital heart defects and liver involvement, are more variable (summary by Huppke et al., 2017).

Neurodevelopmental disorder with microcephaly, seizures, and cortical atrophy (NDMSCA) is an autosomal recessive disorder characterized by severe global developmental delay with poor motor and intellectual function apparent soon after birth, as well as postnatal progressive microcephaly. Most patients develop early-onset, frequent, and often intractable seizures, compatible with an epileptic encephalopathy. Other features include poor feeding, poor overall growth, absent speech, poor or absent eye contact, inability to achieve walking, hypotonia, and peripheral spasticity. Brain imaging usually shows progressive cerebral atrophy, thin corpus callosum, and abnormalities in myelination. Death in childhood may occur (summary by Siekierska et al., 2019).

Congenital disorder of glycosylation with defective fucosylation is an autosomal recessive multisystem disorder apparent from birth. Affected infants have poor growth, failure to thrive, hypotonia, skeletal anomalies, and delayed psychomotor development with intellectual disability. Additional highly variable congenital defects may be observed (summary by Ng et al., 2018). Genetic Heterogeneity of Congenital Disorders of Glycosylation with Defective Fucosylation See also CDGF2 (618323), caused by mutation in the FCSK gene (608675) on chromosome 16q22. For an overview of congenital disorders of glycosylation (CDG), see CDG1A (212065) and CDG2A (212066).

Primary ciliary dyskinesia-39 (CILD39) is an autosomal recessive disorder characterized by chronic sinopulmonary infections beginning soon after birth and laterality defects in about 50% of patients. Although patient nasal ciliary samples have normal structure, detailed studies may show ciliary kinetic defects in some patients (summary by Bonnefoy et al., 2018). For a phenotypic description and a discussion of genetic heterogeneity of primary ciliary dyskinesia, see 244400.

Susceptibility to acute infection-induced encephalopathy-9 (IIAE9) is an autosomal recessive disorder characterized by episodic acute neurodegeneration and developmental regression associated with infections and febrile illness. Patients present in the first months or years of life, often after normal or only mildly delayed early development. Some patients may have partial recovery between episodes, such as transient ataxia, but the overall disease course is progressive, resulting in global developmental delay, abnormal movements, refractory seizures, microcephaly, and cerebellar atrophy (summary by Fichtman et al., 2019). For a discussion of genetic heterogeneity of susceptibility to acute infection-induced encephalopathy, see 610551.

Immunodeficiency-62 (IMD62) is an autosomal recessive primary immunologic disorder clinically characterized by onset of recurrent upper and lower respiratory infections late in the first decade of life. Patients may also have increased viral susceptibility to varicella zoster virus (VZV) or herpes simplex virus (HSV). Laboratory studies show impaired antibody response to vaccination, low levels of circulating memory B cells, and almost undetectable antibodies. There is also evidence of secondary T-cell dysfunction. The disorder may result from disturbed actin cytoskeleton dynamics causing impaired lymphocyte migration (summary by Bouafia et al., 2019).

Immunodeficiency-64 with lymphoproliferation (IMD64) is an autosomal recessive primary immunodeficiency characterized by onset of recurrent bacterial, viral, and fungal infections in early childhood. Laboratory studies show variably decreased numbers of T cells, with lesser deficiencies of B and NK cells. There is impaired T-cell proliferation and activation; functional defects in B cells and NK cells may also be observed. Patients have increased susceptibility to EBV infection and may develop lymphoproliferation or EBV-associated lymphoma. Some patients may develop features of autoimmunity (summary by Salzer et al., 2016, Mao et al., 2018, and Winter et al., 2018).

Primary ciliary dyskinesia-43 (CILD43) is a disorder characterized by a defect in motile cilia and ciliary clearance resulting in the onset of respiratory insufficiency soon after birth, and associated with recurrent upper and lower respiratory infections with chronic progressive lung disease. Patients with this disorder also develop significant obstructive hydrocephalus requiring shunting in infancy, although adult onset of neurologic symptoms may occur. Other more variable features include infertility and about a 50% chance of situs inversus or other left-right asymmetry defects. The disorder is considered to be a type of ciliopathy known as 'reduced generation of multiple motile cilia' (RGMC) (summary by Wallmeier et al., 2019). For a discussion of genetic heterogeneity of primary ciliary dyskinesia, CILD1 (244400).

Immunodeficiency-73B with defective neutrophil chemotaxis (IMD73B) is an autosomal dominant immunologic disorder characterized by onset of recurrent infections in infancy or early childhood. Affected individuals develop respiratory infections, cellulitis, and severe invasive infections or sepsis; organisms include bacteria such as Staphylococcus, as well as viruses, fungi, and mycobacterial species. Laboratory studies show variable abnormalities, including B- and T-cell lymphopenia, decreased immunoglobulin subsets, decreased TRECs and dysfunctional T cells, decreased NK cells, neutropenia, and impaired neutrophil chemotaxis. Hematopoietic stem cell transplantation is curative (summary by Hsu et al., 2019; review by Lougaris et al., 2020). In a review of autosomal forms of chronic granulomatous disease (see 306400 for genetic heterogeneity of CGD), Roos et al. (2021) noted that patients with RAC2 mutations may manifest CGD-like symptoms due to defects in neutrophil NADPH oxidase activity.

Mitochondrial complex I deficiency nuclear type 36 (MC1DN36) is an autosomal recessive metabolic disorder characterized by global developmental delay, hypotonia, and failure to thrive apparent from infancy or early childhood. Affected individuals usually do not acquire ambulation, show progressive spasticity, and have impaired intellectual development with absent speech. More variable features may include pale optic discs, poor eye contact, seizures, and congenital heart defects. Laboratory studies show increased serum lactate; metabolic acidosis may occur during stress or infection. Brain imaging shows T2-weighted abnormalities in the basal ganglia and brainstem, consistent with a clinical diagnosis of Leigh syndrome (see 256000). Patient tissue showed isolated mitochondrial complex I deficiency. Death may occur in childhood (Alahmad et al., 2020). For a discussion of genetic heterogeneity of mitochondrial complex I deficiency, see 252010.

Immunodeficiency-78 with autoimmunity and developmental delay (IMD78) is an autosomal recessive systemic disorder characterized by onset of symptoms in early childhood. Affected individuals present with features of immune deficiency, such as recurrent sinopulmonary or skin infections, as well as autoimmunity, including autoimmune cytopenias, hemolytic anemia, and thrombocytopenia. Autoimmune hepatitis or thyroid disease and central nervous system vasculitis with stroke may also occur. There is increased susceptibility to bacterial, viral, and fungal infections. Laboratory studies show lymphopenia with advanced differentiation and premature senescence of CD8+ T cells and B cells; some patients may have hypergammaglobulinemia. The findings indicate immune dysregulation. Patients also have global developmental delay with speech delay and variable intellectual disability. Many patients die prematurely, but successful hematopoietic bone marrow transplant may be curative (summary by Lu et al., 2014 and Atallah et al., 2021).

Den Hoed-de Boer-Voisin syndrome (DHDBV) is characterized by global developmental delay with moderately to severely impaired intellectual development, poor or absent speech, and delayed motor skills. Although the severity of the disorder varies, many patients are nonverbal and have hypotonia with inability to sit or walk. Early-onset epilepsy is common and may be refractory to treatment, leading to epileptic encephalopathy and further interruption of developmental progress. Most patients have feeding difficulties with poor overall growth and dysmorphic facial features, as well as significant dental anomalies resembling amelogenesis imperfecta. The phenotype is reminiscent of Kohlschutter-Tonz syndrome (KTZS; 226750). More variable features of DHDBV include visual defects, behavioral abnormalities, and nonspecific involvement of other organ systems (summary by den Hoed et al., 2021).

Retinal dystrophy and microvillus inclusion disease (RDMVID) is characterized by early-onset severe retinal dystrophy in association with intractable congenital diarrhea requiring total parenteral nutrition (TPN). Intestinal biopsies show typical features of microvillus inclusion disease (MVID), including loss of microvilli, microvillus inclusions, and accumulation of subapical vesicles in epithelial cells (Janecke et al., 2021). Because STX3 isoform B (STX3B) predominates in the retina, mutations in the STX3 gene that affect both isoform A (STX3A) and STX3B cause both retinal and gastrointestinal disease (RDMVID), whereas mutations in STX3 affecting only the STX3A transcript cause only diarrhea (DIAR12; 619445).

Biliary, renal, neurologic, and skeletal syndrome (BRENS) is an autosomal recessive complex ciliopathy with multisystemic manifestations. The most common presentation is severe neonatal cholestasis that progresses to liver fibrosis and cirrhosis. Most patients have additional clinical features suggestive of a ciliopathy, including postaxial polydactyly, hydrocephalus, retinal abnormalities, and situs inversus. Additional features of the syndrome may include congenital cardiac defects, echogenic kidneys with renal failure, ocular abnormalities, joint hyperextensibility, and dysmorphic facial features. Some patients have global developmental delay. Brain imaging typically shows dilated ventricles, hypomyelination, and white matter abnormalities, although some patients have been described with abnormal pituitary development (summary by Shaheen et al., 2020 and David et al., 2020).

Immunodeficiency-89 and autoimmunity (IMD89) is an autosomal recessive immune disorder characterized by adult onset of recurrent infections, allergies, microcytic anemia, and Crohn disease (see 266600) (Yang et al., 2020).

Immunodeficiency-91 and hyperinflammation (IMD91) is an autosomal recessive complex immunologic disorder characterized by both immunodeficiency and recurrent infections, often to viruses or mycobacteria, as well as by hyperinflammation with systemic involvement. Affected individuals present in infancy with variable features, including fever, infection, thrombocytopenia, renal or hepatic dysfunction, recurrent infections, or seizures. Most patients eventually develop hepatic or renal failure, compromised neurologic function, lymphadenopathy or hepatosplenomegaly, and multiorgan failure resulting in death. More variable features may include intermittent monocytosis, features of hemophagocytic lymphohistiocytosis (HLH), and serologic evidence of hyperinflammation. The disorder is thought to result from dysregulation of the interferon response to viral stimulation in the innate immune system (summary by Le Voyer et al., 2021; Vavassori et al., 2021).

Immunodeficiency-102 (IMD102) is an X-linked recessive immunologic disorder characterized by the onset of recurrent sinopulmonary, mucosal, and other infections in early childhood, usually accompanied by refractory autoimmune cytopenias. Affected individuals have bacterial, viral, and fungal infections, as well as hemolytic anemia, thrombocytopenia, lymphopenia, and decreased NK cells. Laboratory studies show defective T-cell proliferation and function, likely due to signaling abnormalities. The disorder may also manifest as a hyperinflammatory state with immune dysregulation (Delmonte et al., 2021).

Immunodeficiency-96 (IMD96) is an autosomal recessive disorder characterized by onset of recurrent, usually viral, respiratory infections in infancy or early childhood. Other infections, including gastrointestinal and urinary tract infections, may also occur. Laboratory studies show hypogammaglobulinemia, lymphopenia with increased gamma/delta T cells, and erythrocyte macrocytosis. The disorder results from defective cellular DNA repair (summary by Maffucci et al., 2018).

Neurodevelopmental disorder with poor growth, large ears, and dysmorphic facies (NEDGEF) is an autosomal recessive disorder characterized by these features as well as hypotonia and global developmental delay with impaired intellectual development. The severity is variable, even within families. Death in early childhood has been reported in 1 family (Alsaif et al., 2021).

Recurrent respiratory infections and failure to thrive with or without diarrhea (RIFTD) is characterized by neonatal onset of chronic cough, episodic wheezing, recurrent lower respiratory tract infections, chronic diarrhea, and failure to thrive. Despite the resemblance to cystic fibrosis (CF; 219700), these patients have normal sweat chloride and pancreatic elastase tests (Bertoli-Avella et al., 2022).

Immunodeficiency-109 with EBV-induced lymphoproliferation (IMD109) is an autosomal recessive primary immune disorder characterized by onset of recurrent sinopulmonary infections in childhood. Affected individuals are susceptible to infection with EBV and develop EBV viremia and EBV-associated lymphoproliferative disease or B-cell lymphoma. Immunologic work-up shows normal levels of T, B, and NK cells, with defective CD8+ T cell function after stimulation. Some patients may have hypogammaglobulinemia and poor antibody response to stimulation (Alosaimi et al., 2019).

C1q deficiency (C1QD) is a rare autosomal recessive disorder characterized by recurrent skin lesions, chronic infections, and an increased risk of autoimmune diseases, particularly systemic lupus erythematosus (SLE; see 152700) or SLE-like diseases. It has also been associated with chronic glomerulonephritis and renal failure. C1q deficiency presents in 2 different forms, absent C1q protein or presence of a dysfunctional molecule (summary by Topaloglu et al., 1996 and Vassallo et al., 2007). For a discussion of genetic heterogeneity of C1q deficiency, see 613652.

Infantile-onset multisystem autoimmune disease-3 (ADMIO3) is an autosomal recessive disorder of immune dysregulation characterized by the onset of various systemic autoimmune manifestations in the first months or years of life. Features may include hypothyroidism, type 1 diabetes mellitus, systemic inflammatory manifestations (fever, hepatomegaly), and autoimmune cytopenias. Laboratory studies show normal levels of T, B, and NK cells, but CD4+ (see 186940) T cells demonstrate hyperproliferation when stimulated in vitro (Janssen et al., 2022). For a discussion of genetic heterogeneity of ADMIO, see ADMIO1 (615952).

Immunodeficiency-112 (IMD112) is an autosomal recessive primary immunologic disorder with variable manifestations beginning in early childhood. Some patients have recurrent bacterial, viral, and fungal infections, including disseminated bacillus Calmette-Guerin (BCG)-related infections, whereas at least 1 patient only presented with BCG-related infections. Immunologic workup shows variable abnormalities affecting lymphoid immunity, including hypogammaglobulinemia, lymphopenia or paradoxical lymphocytosis, and defects in B, T, and NK cell differentiation and function mainly due to disruption of the noncanonical NFKB (see 164011) signaling pathway (Willmann et al., 2014; Schlechter et al., 2017).