Familial Mediterranean fever (FMF) is divided into two phenotypes: type 1 and type 2. FMF type 1 is characterized by recurrent short episodes of inflammation and serositis including fever, peritonitis, synovitis, pleuritis, and, rarely, pericarditis and meningitis. The symptoms and severity vary among affected individuals, sometimes even among members of the same family. Amyloidosis, which can lead to renal failure, is the most severe complication, if untreated. FMF type 2 is characterized by amyloidosis as the first clinical manifestation of FMF in an otherwise asymptomatic individual.

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.

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.

Chronic infantile neurologic cutaneous and articular syndrome (CINCA) is an early-onset, severe, chronic inflammatory disease, characterized by cutaneous symptoms, central nervous system involvement, and arthropathy (Feldmann et al., 2002). See also familial cold autoinflammatory syndrome-1 (FCAS1, CAPS1; 120100), an allelic disorder with a less severe phenotype.

IGHD3 is characterized by agammaglobulinemia and markedly reduced numbers of B cells, short stature, delayed bone age, and good response to treatment with growth hormone (summary by Conley et al., 1991). For general phenotypic information and a discussion of genetic heterogeneity of IGHD, see 262400.

Severe combined immunodeficiency refers to a genetically and clinically heterogeneous group of disorders with defective cellular and humoral immune function. Patients with SCID present in infancy with recurrent, persistent infections by opportunistic organisms, including Candida albicans, Pneumocystis carinii, and cytomegalovirus, among many others. Laboratory analysis shows profound lymphopenia with diminished or absent immunoglobulins. The common characteristic of all types of SCID is absence of T cell-mediated cellular immunity due to a defect in T-cell development. Without treatment, patients usually die within the first year of life. The overall prevalence of all types of SCID is approximately 1 in 75,000 births (Fischer et al., 1997; Buckley, 2004). Genetic Heterogeneity of SCID SCID can be divided into 2 main classes: those with B lymphocytes (B+ SCID) and those without (B- SCID). Presence or absence of NK cells is variable within these groups. The most common form of SCID is X-linked T-, B+, NK- SCID (SCIDX1; 300400) caused by mutation in the IL2RG gene (308380) on chromosome Xq13.1. Autosomal recessive SCID includes T-, B-, NK+ SCID, caused by mutation in the RAG1 and RAG2 genes on 11p13; T-, B+, NK- SCID (600802), caused by mutation in the JAK3 gene (600173) on 19p13; T-, B+, NK+ SCID (IMD104; 608971), caused by mutation in the IL7R gene (146661) on 5p13; T-, B+, NK+ SCID (IMD105; 619924), caused by mutation in the CD45 gene (PTPRC; 151460) on 1q31-q32; T-, B+, NK+ SCID (IMD19; 615617), caused by mutation in the CD3D gene (186790) on 11q23; T-, B-, NK- SCID (102700) caused by mutation in the ADA (608958) gene on 20q13; and T-, B-, NK+ SCID with sensitivity to ionizing radiation (602450), caused by mutation in the Artemis gene (DCLRE1C; 605988) on 10p13 (Kalman et al., 2004); and T-, B-, NK+ SCID with microcephaly, growth retardation, and sensitivity to ionizing radiation (611291), caused by mutation in the NHEJ1 gene (611290) on 2q35. Approximately 20 to 30% of all SCID patients are T-, B-, NK+, and approximately half of these patients have mutations in the RAG1 or RAG2 genes (Schwarz et al., 1996; Fischer et al., 1997).

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.

Sacral defect with anterior meningocele (SDAM) is a form of caudal dysgenesis. It is present at birth and becomes symptomatic later in life, usually because of obstructive labor in females, chronic constipation, or meningitis. Inheritance is autosomal dominant (Chatkupt et al., 1994). Welch and Aterman (1984) gave a population frequency of 0.14%. Caudal dysgenesis syndrome and caudal regression syndrome are broad terms that refer to a heterogeneous constellation of congenital caudal anomalies affecting the caudal spine and spinal cord, the hindgut, the urogenital system, and the lower limbs. Approximately 15 to 25% of mothers of children with caudal dysgenesis have insulin-dependent diabetes mellitus (222100) (Lynch et al., 2000). See also Currarino syndrome (176450), a similar disorder caused by mutation in the HLXB9 gene (142994) on chromosome 7q36. Currarino syndrome classically comprises the triad of hemisacrum, anorectal malformation, and presacral mass. However, Currarino syndrome also shows phenotypic variability: Lynch et al. (2000) stated that there is variable expressivity of clinical features and that some patients with Currarino syndrome are asymptomatic. Kochling et al. (2001) found the complete triad of Currarino syndrome in only 8 of 23 patients with mutations in the HLXB9 gene, These reports suggest that some patients previously reported as having forms of sacral agenesis, including SDAM, may have had Currarino syndrome and vice versa. See also spina bifida (182940), which can be seen in some patients with sacral agenesis or caudal regression syndrome and may be etiologically related.

Immunodeficiency-67 (IMD67) is an autosomal recessive primary immunodeficiency characterized by recurrent severe systemic and invasive bacterial infections beginning in infancy or early childhood. The most common organisms implicated are Streptococcus pneumoniae and Staphylococcus aureus; Pseudomonas and atypical Mycobacteria may also be observed. IMD67 is life-threatening in infancy and early childhood. The first invasive infection typically occurs before 2 years of age, with meningitis representing up to 41% of the bacterial infections. The mortality rate in early childhood is high, with most deaths occurring before 8 years of age. Affected individuals have an impaired inflammatory response to infection, including lack of fever and neutropenia, although erythrocyte sedimentation rate (ESR) and C-reactive protein may be elevated. General immunologic workup tends to be normal, with normal levels of B cells, T cells, and NK cells. However, more detailed studies indicate impaired cytokine response to lipopolysaccharide (LPS) and IL1B (147720) stimulation; response to TNFA (191160) is usually normal. Patients have good antibody responses to most vaccinations, with the notable exception of pneumococcal vaccination. Viral, fungal, and parasitic infections are not generally observed. Early detection is critical in early childhood because prophylactic treatment with IVIg or certain antibiotics is effective; the disorder tends to improve naturally around adolescence. At the molecular level, the disorder results from impaired function of selective Toll receptor (see TLR4, 603030)/IL1R (see IL1R1, 147810) signaling pathways that ultimately activate NFKB (164011) to produce cytokines (summary by Ku et al., 2007; Picard et al., 2010; Grazioli et al., 2016). See also IMD68 (612260), caused by mutation in the MYD88 gene (602170), which shows a similar phenotype to IMD67. As the MYD88 and IRAK4 genes interact in the same intracellular signaling pathway, the clinical and cellular features are almost indistinguishable (summary by Picard et al., 2010).

A rare genetic primary immunodeficiency with characteristics of increased susceptibility to fungal infections that typically manifest as recurrent, chronic mucocutaneous candidiasis, systemic candidiasis with meningoencephalitis and deep dermatophytosis. Dermatophytes invade skin, hair, nails, lymph nodes and brain, resulting in erythematosquamous lesions, nodular subcutaneous or ulcerative infiltrations, severe onychomycosis and lymphadenopathy.

Familial hemophagocytic lymphohistiocytosis-2 (FHL2) is an autosomal recessive disorder of immune dysregulation with onset in infancy or early childhood. It is characterized clinically by fever, edema, hepatosplenomegaly, and liver dysfunction. Neurologic impairment, seizures, and ataxia are frequent. Laboratory studies show pancytopenia, coagulation abnormalities, hypofibrinogenemia, and hypertriglyceridemia. There is increased production of cytokines, such as gamma-interferon (IFNG; 147570) and TNF-alpha (191160), by hyperactivation and proliferation of T cells and macrophages. Activity of cytotoxic T cells and NK cells is reduced, consistent with a defect in cellular cytotoxicity. Bone marrow, lymph nodes, spleen, and liver show features of hemophagocytosis. Chemotherapy and/or immunosuppressant therapy may result in symptomatic remission, but the disorder is fatal without bone marrow transplantation (summary by Dufourcq-Lagelouse et al., 1999, Stepp et al., 1999, and Molleran Lee et al., 2004). For a general phenotypic description and a discussion of genetic heterogeneity of FHL, see 267700.

Immunodeficiency-83 (IMD83) is characterized by increased susceptibility to severe viral infections, including herpes simplex virus (HSV), varicella zoster virus (VZV), influenza A virus (IAV), hantavirus, and possibly respiratory syncytial virus (RSV). The age at onset varies widely from infancy to adulthood, and there is incomplete penetrance. The susceptibility to encephalitis or pneumonitis appears to result from impaired TLR3-dependent interferon production by nonhematopoietic cells that reside within the central nervous system (CNS) or lung epithelial cells (review by Zhang et al., 2013; summary by Mork et al., 2015; Sironi et al., 2017, Lim et al., 2019, Partanen et al., 2020). For a general phenotypic description of herpes simplex encephalitis and a discussion of genetic heterogeneity of acute infection-induced encephalopathy, see 610551.

Any autosomal agammaglobulinemia in which the cause of the disease is a mutation in the IGLL1 gene.

Patients with deficiency of C8 suffer from recurrent neisserial infections, predominantly with meningococcus infection of rare serotypes. Most such patients are discovered among those having their first episode of meningitis at ages older than 10 years (Ross and Densen, 1984). Two types of inherited C8 deficiency have been reported in humans: type I (613790), in which only C8 alpha (C8A, 120950) and C8 gamma (C8G; 120930) are deficient, and type II, in which only C8 beta is deficient (Marcus et al., 1982; Tedesco et al., 1983). The 2 types are clinically indistinguishable (Ross and Densen, 1984).

Patients with deficiency of C8 suffer from recurrent neisserial infections, predominantly with meningococcus infection of rare serotypes. Most such patients are discovered among those having their first episode of meningitis at ages older than 10 years (Ross and Densen, 1984). Two kinds of inherited C8 deficiency have been reported in humans: type I (C8D1), in which only C8 alpha and C8 gamma (C8G; 120930) are deficient, and type II (C8D2; 613789), in which only C8 beta (C8B; 120960) is deficient (Marcus et al., 1982; Tedesco et al., 1983). The 2 types are clinically indistinguishable (Ross and Densen, 1984).

Concentration of the complement component C4b in the blood circulation below the lower limit of normal.

Autoinflammation with infantile enterocolitis is an autosomal dominant disorder characterized by onset of recurrent flares of autoinflammation in early infancy. Affected individuals tend to have poor overall growth and gastrointestinal symptoms in infancy associated with laboratory evidence of activated inflammation. This initial presentation is followed by recurrent febrile episodes with splenomegaly and sometimes hematologic disturbances, arthralgias, or myalgias. The disorder results from overactivation of an arm of the immune response system (Romberg et al., 2014; Canna et al., 2014).

Immunodeficiency-71 with inflammatory disease and congenital thrombocytopenia (IMD71) is an autosomal recessive immunologic disorder characterized by the onset of recurrent infections and inflammatory features such as vasculitis and eczema in infancy or early childhood. Infectious agents include bacteria and viruses. Laboratory findings are variable, but usually show thrombocytopenia, sometimes with abnormal platelet morphology, increased serum IgE, IgA, or IgM, leukocytosis, decreased or increased T lymphocytes, and increased eosinophils. Detailed studies show impaired neutrophil and T-cell chemotaxis, as well as impaired T-cell activation due to defects in F-actin (see 102610) polymerization (summary by Brigida et al., 2018).

Familial Hemophagocytic lymphohistiocytosis (FHL) is a rare primary immunodeficiency characterized by a macrophage activation syndrome with an onset usually occurring within a few months or less common several years after birth.

Immunodeficiency-66 (IMD66) is an autosomal recessive primary immune disorder caused by defective immune cell migration and chemotaxis resulting from defects in cytoskeletal actin dynamics. Neutrophils are primarily affected, although there may be defects in dendritic cells and T and B cells. The phenotype is characterized by onset of recurrent bacterial infections in infancy. Laboratory studies show normal levels of myeloid and lymphoid cells, but there may be mild thrombocytopenia (summary by Record et al., 2015).

X-linked lymphoproliferative disease (XLP) has two recognizable subtypes, XLP1 and XLP2. XLP1 is characterized predominantly by one of three commonly recognized phenotypes: Inappropriate immune response to Epstein-Barr virus (EBV) infection leading to hemophagocytic lymphohistiocytosis (HLH) or severe mononucleosis. Dysgammaglobulinemia. Lymphoproliferative disease (malignant lymphoma). XLP2 is most often characterized by HLH (often associated with EBV), dysgammaglobulinemia, and inflammatory bowel disease. HLH resulting from EBV infection is associated with an unregulated and exaggerated immune response with widespread proliferation of cytotoxic T cells, EBV-infected B cells, and macrophages. Dysgammaglobulinemia is typically hypogammaglobulinemia of one or more immunoglobulin subclasses. The malignant lymphomas are typically B-cell lymphomas, non-Hodgkin type, often extranodal, and in particular involving the intestine.

A rare genetic combined T and B cell immunodeficiency characterised by life-threatening infections due to disrupted transferrin receptor 1 endocytosis, resulting in defective cellular iron transport and impaired T and B cell function. Patients present with early-onset chronic diarrhoea, severe recurrent infections and failure to thrive. Laboratory studies reveal hypo or agammaglobulinaemia, normal lymphocyte counts but decreased numbers of memory B cells, intermittent neutropenia and thrombocytopenia, and mild anaemia (resistant to iron supplementation) with low mean corpuscular volume.

Autosomal dominant agammaglobulinemia-10 (AGM10) is characterized by early-childhood onset of recurrent viral and bacterial infections affecting various organ systems, particularly the sinopulmonary system. Laboratory studies show low or absent circulating B cells and hypo- or agammaglobulinemia. Affected individuals may have adverse reactions to certain vaccinations, such as the polio vaccine. Treatment with replacement Ig is effective; hematopoietic stem cell transplantation has also been reported (summary by Le Coz et al., 2021). For a discussion of genetic heterogeneity of autosomal agammaglobulinemia, see AGM1 (601495).