Alkaptonuria is caused by deficiency of homogentisate 1,2-dioxygenase, an enzyme that converts homogentisic acid (HGA) to maleylacetoacetic acid in the tyrosine degradation pathway. The three major features of alkaptonuria are dark urine or urine that turns dark on standing, ochronosis (bluish-black pigmentation in connective tissue), and arthritis of the spine and larger joints. Ochronosis generally occurs after age 30 years; arthritis often begins in the third decade. Other manifestations can include pigment in the sclera, ear cartilage, and skin of the hands; aortic or mitral valve calcification or regurgitation and occasionally aortic dilatation; renal stones; prostate stones; and hypothyroidism.

Behçet disease is an inflammatory condition that affects many parts of the body. The health problems associated with Behçet disease result from widespread inflammation of blood vessels (vasculitis). This inflammation most commonly affects small blood vessels in the mouth, genitals, skin, and eyes.\n\nPainful mouth sores called aphthous ulcers are usually the first sign of Behçet disease. These sores can occur on the lips, tongue, inside the cheeks, the roof of the mouth, the throat, and the tonsils. The ulcers look like common canker sores, and they typically heal within one to two weeks. About 75 percent of all people with Behçet disease develop similar ulcers on the genitals. These ulcers occur most frequently on the scrotum in men and on the labia in women.\n\nBehçet disease can also cause painful bumps and sores on the skin. Most affected individuals develop pus-filled bumps that resemble acne. These bumps can occur anywhere on the body. Some affected people also have red, tender nodules called erythema nodosum. These nodules usually develop on the legs but can also occur on the arms, face, and neck.\n\nAn inflammation of the eye called uveitis is found in more than half of people with Behçet disease. Eye problems are more common in younger people with the disease and affect men more often than women. Uveitis can result in blurry vision and an extreme sensitivity to light (photophobia). Rarely, inflammation can also cause eye pain and redness. If untreated, the eye problems associated with Behçet disease can lead to blindness.\n\nJoint involvement is also common in Behçet disease. Often this affects one joint at a time, with each affected joint becoming swollen and painful and then getting better.\n\nLess commonly, Behçet disease can affect the brain and spinal cord (central nervous system), gastrointestinal tract, large blood vessels, heart, lungs, and kidneys. Central nervous system abnormalities can lead to headaches, confusion, personality changes, memory loss, impaired speech, and problems with balance and movement. Involvement of the gastrointestinal tract can lead to a hole in the wall of the intestine (intestinal perforation), which can cause serious infection and may be life-threatening.\n\nThe signs and symptoms of Behçet disease usually begin in a person's twenties or thirties, although they can appear at any age. Some affected people have relatively mild symptoms that are limited to sores in the mouth and on the genitals. Others have more severe symptoms affecting various parts of the body, including the eyes and the vital organs. The features of Behçet disease typically come and go over a period of months or years. In most affected individuals, the health problems associated with this disorder improve with age.

Systemic lupus erythematosus (SLE) is a complex autoimmune disease characterized by production of autoantibodies against nuclear, cytoplasmic, and cell surface molecules that transcend organ-specific boundaries. Tissue deposition of antibodies or immune complexes induces inflammation and subsequent injury of multiple organs and finally results in clinical manifestations of SLE, including glomerulonephritis, dermatitis, thrombosis, vasculitis, seizures, and arthritis. Evidence strongly suggests the involvement of genetic components in SLE susceptibility (summary by Oishi et al., 2008). Genetic Heterogeneity of Systemic Lupus Erythematosus An autosomal recessive form of systemic lupus erythematosus (SLEB16; 614420) is caused by mutation in the DNASE1L3 gene (602244) on chromosome 3p14.3. An X-linked dominant form of SLE (SLEB17; 301080) is caused by heterozygous mutation in the TLR7 gene (300365) on chromosome Xp22. See MAPPING and MOLECULAR GENETICS sections for a discussion of genetic heterogeneity of susceptibility to SLE.

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.

Congenital vertical talus (CVT), also known as 'rocker-bottom foot' deformity, is a dislocation of the talonavicular joint characterized by vertical orientation of the talus with a rigid dorsal dislocation of the navicular, equinus deformity of the calcaneus, abduction deformity of the forefoot, and contracture of the soft tissues of the hind- and mid-foot. This condition is usually associated with multiple other congenital deformities and only rarely is an isolated deformity with familial occurrence (summary by Levinsohn et al., 2004). The condition is transmitted in an autosomal dominant pattern of inheritance, and sometimes shows incomplete penetrance and variable expressivity. There may be a broad spectrum of deformities, including flatfoot, talipes equinovarus (TEV or clubfoot), cavus foot, metatarsus adductus, and even hypoplasia of the tibia (summary by Dobbs et al., 2006).

The spectrum of ASAH1-related disorders ranges from Farber disease (FD) to spinal muscular atrophy with progressive myoclonic epilepsy (SMA-PME). Classic FD is characterized by onset in the first weeks of life of painful, progressive deformity of the major joints; palpable subcutaneous nodules of joints and mechanical pressure points; and a hoarse cry resulting from granulomas of the larynx and epiglottis. Life expectancy is usually less than two years. In the other less common types of FD, onset, severity, and primary manifestations vary. SMA-PME is characterized by early-childhood-onset progressive lower motor neuron disease manifest typically between ages three and seven years as proximal lower-extremity weakness, followed by progressive myoclonic and atonic seizures, tremulousness/tremor, and sensorineural hearing loss. Myoclonic epilepsy typically begins in late childhood after the onset of weakness and can include jerking of the upper limbs, action myoclonus, myoclonic status, and eyelid myoclonus. Other findings include generalized tremor, and cognitive decline. The time from disease onset to death from respiratory complications is usually five to 15 years.

IPEX (immune dysregulation, polyendocrinopathy, enteropathy, X-linked) syndrome is characterized by systemic autoimmunity, typically beginning in the first year of life. Presentation is most commonly the clinical triad of watery diarrhea, endocrinopathy (most commonly insulin-dependent diabetes mellitus), and eczematous dermatitis. Most children have other autoimmune phenomena including cytopenias, autoimmune hepatitis, or nephropathy; lymphadenopathy, splenomegaly, alopecia, arthritis, and lung disease related to immune dysregulation have all been observed. Fetal presentation of IPEX includes hydrops, echogenic bowel, skin desquamation, IUGR, and fetal akinesia. Without aggressive immunosuppression or bone marrow transplantation, the majority of affected males die within the first one to two years of life from metabolic derangements, severe malabsorption, or sepsis; a few with a milder phenotype have survived into the second or third decade of life.

Mevalonate kinase deficiency is a condition characterized by recurrent episodes of fever, which typically begin during infancy. Each episode of fever lasts about 3 to 6 days, and the frequency of the episodes varies among affected individuals. In childhood the fevers seem to be more frequent, occurring as often as 25 times a year, but as the individual gets older the episodes occur less often.\n\nMevalonate kinase deficiency has additional signs and symptoms, and the severity depends on the type of the condition. There are two types of mevalonate kinase deficiency: a less severe type called hyperimmunoglobulinemia D syndrome (HIDS) and a more severe type called mevalonic aciduria (MVA).\n\nPeople with MVA have signs and symptoms of the condition at all times, not just during episodes of fever. Affected children have developmental delay, problems with movement and balance (ataxia), recurrent seizures (epilepsy), progressive problems with vision, and failure to gain weight and grow at the expected rate (failure to thrive). Individuals with MVA typically have an unusually small, elongated head. In childhood or adolescence, affected individuals may develop eye problems such as inflammation of the eye (uveitis), a blue tint in the white part of the eye (blue sclera), an eye disorder called retinitis pigmentosa that causes vision loss, or clouding of the lens of the eye (cataracts). Affected adults may have short stature and may develop muscle weakness (myopathy) later in life. During fever episodes, people with MVA may have an enlarged liver and spleen (hepatosplenomegaly), lymphadenopathy, abdominal pain, diarrhea, and skin rashes. Children with MVA who are severely affected with multiple problems may live only into early childhood; mildly affected individuals may have a normal life expectancy.\n\nDuring episodes of fever, people with HIDS typically have enlargement of the lymph nodes (lymphadenopathy), abdominal pain, joint pain, diarrhea, skin rashes, and headache. Occasionally they will have painful sores called aphthous ulcers around their mouth. In females, these may also occur around the vagina. Rarely, people with HIDS develop a buildup of protein deposits (amyloidosis) in the kidneys that can lead to kidney failure. Fever episodes in individuals with HIDS can be triggered by vaccinations, surgery, injury, or stress. Most people with HIDS have abnormally high levels of immune system proteins called immunoglobulin D (IgD) and immunoglobulin A (IgA) in the blood. It is unclear why some people with HIDS have high levels of IgD and IgA and some do not. Elevated levels of these immunoglobulins do not appear to cause any signs or symptoms. Individuals with HIDS do not have any signs and symptoms of the condition between fever episodes and typically have a normal life expectancy.

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.

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).

Mitochondrial DNA (mtDNA)-associated Leigh syndrome and NARP (neurogenic muscle weakness, ataxia, and retinitis pigmentosa) are part of a continuum of progressive neurodegenerative disorders caused by abnormalities of mitochondrial energy generation. Leigh syndrome (or subacute necrotizing encephalomyelopathy) is characterized by onset of symptoms typically between ages three and 12 months, often following a viral infection. Decompensation (often with elevated lactate levels in blood and/or CSF) during an intercurrent illness is typically associated with psychomotor retardation or regression. Neurologic features include hypotonia, spasticity, movement disorders (including chorea), cerebellar ataxia, and peripheral neuropathy. Extraneurologic manifestations may include hypertrophic cardiomyopathy. About 50% of affected individuals die by age three years, most often as a result of respiratory or cardiac failure. NARP is characterized by proximal neurogenic muscle weakness with sensory neuropathy, ataxia, and pigmentary retinopathy. Onset of symptoms, particularly ataxia and learning difficulties, is often in early childhood. Individuals with NARP can be relatively stable for many years, but may suffer episodic deterioration, often in association with viral illnesses.

Systemic lupus erythematosus (SLE) is a chronic disease that causes inflammation in connective tissues, such as cartilage and the lining of blood vessels, which provide strength and flexibility to structures throughout the body. The signs and symptoms of SLE vary among affected individuals, and can involve many organs and systems, including the skin, joints, kidneys, lungs, central nervous system, and blood-forming (hematopoietic) system. SLE is one of a large group of conditions called autoimmune disorders that occur when the immune system attacks the body's own tissues and organs.\n\nSLE may first appear as extreme tiredness (fatigue), a vague feeling of discomfort or illness (malaise), fever, loss of appetite, and weight loss. Most affected individuals also have joint pain, typically affecting the same joints on both sides of the body, and muscle pain and weakness. Skin problems are common in SLE. A characteristic feature is a flat red rash across the cheeks and bridge of the nose, called a "butterfly rash" because of its shape. The rash, which generally does not hurt or itch, often appears or becomes more pronounced when exposed to sunlight. Other skin problems that may occur in SLE include calcium deposits under the skin (calcinosis), damaged blood vessels (vasculitis) in the skin, and tiny red spots called petechiae. Petechiae are caused by a shortage of cells involved in clotting (platelets), which leads to bleeding under the skin. Affected individuals may also have hair loss (alopecia) and open sores (ulcerations) in the moist lining (mucosae) of the mouth, nose, or, less commonly, the genitals.\n\nPeople with SLE have episodes in which the condition gets worse (exacerbations) and other times when it gets better (remissions). Overall, SLE gradually gets worse over time, and damage to the major organs of the body can be life-threatening.\n\nAbout a third of people with SLE develop kidney disease (nephritis). Heart problems may also occur in SLE, including inflammation of the sac-like membrane around the heart (pericarditis) and abnormalities of the heart valves, which control blood flow in the heart. Heart disease caused by fatty buildup in the blood vessels (atherosclerosis), which is very common in the general population, is even more common in people with SLE. The inflammation characteristic of SLE can also damage the nervous system, and may result in abnormal sensation and weakness in the limbs (peripheral neuropathy); seizures; stroke; and difficulty processing, learning, and remembering information (cognitive impairment). Anxiety and depression are also common in SLE.

A rare pleiotropic auto-inflammatory disorder of childhood, primarily affecting the joints and skin. The first affected family contained ten affected members from three generations and manifested variable expression of a pauciarticular, nonaxial, arthritis that began in childhood; pyoderma gangrenosum; and severe cystic acne in adolescence and beyond. Recurrent sterile arthritis usually occurs after minor trauma, but can also occur spontaneously. PAPA syndrome is a self-limiting disease, but it can lead to severe joint destruction. The gene responsible for the syndrome is the proline-serine-threonine phosphatase interacting protein 1 (PSTPIP1).

TFR2-related hereditary hemochromatosis (TFR2-HHC) is characterized by increased intestinal iron absorption resulting in iron accumulation in the liver, heart, pancreas, and endocrine organs. Age of onset is earlier than in HFE-HHC. The majority of individuals present with signs and symptoms of iron overload in the third decade (e.g., weakness, fatigue, abdominal pain, hepatomegaly, arthritis, arthralgia, progressive increase in skin pigmentation). Others present as young adults with nonspecific symptoms and abnormal serum iron studies or as adults with abnormal serum iron studies and signs of organ involvement including cirrhosis, diabetes mellitus, and arthropathy.

The camptodactyly-arthropathy-coxa vara-pericarditis syndrome (CACP) is an autosomal recessive condition characterized by the association of congenital or early-onset camptodactyly and noninflammatory arthropathy with synovial hyperplasia. Progressive coxa vara deformity and/or noninflammatory pericardial or pleural effusions are found in some patients (summary by Faivre et al., 2000).

Juvenile hemochromatosis is characterized by onset of severe iron overload occurring typically in the first to third decades of life. Males and females are equally affected. Prominent clinical features include hypogonadotropic hypogonadism, cardiomyopathy, glucose intolerance and diabetes, arthropathy, and liver fibrosis or cirrhosis. Hepatocellular cancer has been reported occasionally. The main cause of death is cardiac disease. If juvenile hemochromatosis is detected early enough and if blood is removed regularly through the process of phlebotomy to achieve iron depletion, morbidity and mortality are greatly reduced.

Autosomal domiant spondyloepiphyseal dysplasia tarda (autosomal dominant SEDT) is an inherited condition that affects bone growth. Signs and symptoms are generally physically apparent by puberty; however, abnormalities may be seen on X-ray at an earlier age. Affected people may have skeletal abnormalities, short stature (with a short neck and trunk, specifically), scoliosis, kyphosis, lumbar hyperlordosis (exaggerated curvature of the lower back), and early-onset progressive osteoarthritis of the hips and knees. Some cases of autosomal dominant SEDT may be caused by changes (mutations) in the COL2A1 gene. As the name suggests, the condition is inherited in an autosomal dominant manner. Treatment is based on the signs and symptoms present in each person and may include surgery and pain management strategies.

Psoriasis (psoriasis vulgaris; PV) is a chronic inflammatory dermatosis that affects approximately 2% of the population. It is characterized by red, scaly skin patches that are usually found on the scalp, elbows, and knees, and may be associated with severe arthritis. The lesions are caused by abnormal keratinocyte proliferation and infiltration of inflammatory cells into the dermis and epidermis. The usual age of onset of psoriasis is between 15 and 30 years, although it can present at any age (summary by Matthews et al., 1996). Generalized pustular psoriasis (GPP) is a life-threatening disease characterized by sudden, repeated episodes of high-grade fever, generalized rash, and disseminated pustules, with hyperleukocytosis and elevated serum levels of C-reactive protein (123260) (summary by Marrakchi et al., 2011). GPP often presents in patients with existing or prior psoriasis vulgaris; however, GPP can develop without a history of PV (Sugiura et al., 2013). Palmoplantar pustulosis and acrodermatitis continua of Hallopeau represent acral forms of pustular psoriasis that have historically been grouped with GPP (summary by Setta-Kaffetzi et al., 2013). Nestle et al. (2009) provided a detailed review of the pathogenesis and genetics of psoriasis. Genetic Heterogeneity of Psoriasis and Psoriasis Susceptibility PSORS2 (602723) is caused by mutation in the CARD14 gene (607211) on chromosome 17q25, and PSORS14 (614204) is caused by mutation in the IL36RN gene (605507) on chromosome 2q14. Psoriasis susceptibility loci include PSORS1 on 6p21.3; PSORS3 (601454) on 4q; PSORS4 on 1q21; PSORS5 (604316) on 3q21; PSORS6 (605364) on 19p; PSORS7 (605606) on 1p; PSORS8 (610707) on 16q; PSORS9 (607857) on 4q31; PSORS10 (612410) on 18p11; PSORS11 (612599) on 5q31-q33; PSORS12 (612950) on 20q13; PSORS13 (614070), conferred by variation in the TRAF3IP2 gene (607043) on 6q21; and PSORS15 (616106), conferred by variation in the AP1S3 gene (615781) on 2q36. An additional putative psoriasis candidate locus has been reported on 20p (Nair et al., 1997).

Stickler syndrome is a connective tissue disorder that can include ocular findings of myopia, cataract, and retinal detachment; hearing loss that is both conductive and sensorineural; midfacial underdevelopment and cleft palate (either alone or as part of the Robin sequence); and mild spondyloepiphyseal dysplasia and/or precocious arthritis. Variable phenotypic expression of Stickler syndrome occurs both within and among families; interfamilial variability is in part explained by locus and allelic heterogeneity.

Familial cold autoinflammatory syndrome-2 (FCAS2) is an autosomal dominant autoinflammatory disorder characterized by episodic and recurrent rash, urticaria, arthralgia, myalgia, and headache. In most patients, these episodes are accompanied by fever and serologic evidence of inflammation. Most, but not all, patients report exposure to cold as a trigger for the episodes. Additional features may include abdominal pain, thoracic pain, and sensorineural deafness. The age at onset is variable, ranging from the first year of life to middle age, and the severity and clinical manifestations are heterogeneous (summary by Shen et al., 2017). For a phenotypic description and a discussion of genetic heterogeneity of familial cold autoinflammatory syndrome, see FCAS1 (120100).

Any sarcoidosis in which the cause of the disease is a mutation in the HLA-DRB1 gene.

Sitosterolemia is characterized by: Hypercholesterolemia (especially in children) which (1) shows an unexpected significant lowering of plasma cholesterol level in response to low-fat diet modification or to bile acid sequestrant therapy; or (2) does not respond to statin therapy; Tendon xanthomas or tuberous (i.e., planar) xanthomas that can occur in childhood and in unusual locations (heels, knees, elbows, and buttocks); Premature atherosclerosis, which can lead to angina, aortic valve involvement, myocardial infarction, and sudden death; Hemolytic anemia, abnormally shaped erythrocytes (stomatocytes), and large platelets (macrothrombocytopenia). On occasion, the abnormal hematologic findings may be the initial presentation or the only clinical feature of this disorder. Arthritis, arthralgias, and splenomegaly may sometimes be seen and one study has concluded that "idiopathic" liver disease could be undiagnosed sitosterolemia. The clinical spectrum of sitosterolemia is probably not fully appreciated due to underdiagnosis and the fact that the phenotype in infants is likely to be highly dependent on diet.

Roifman-Chitayat syndrome (ROCHIS) is an autosomal recessive digenic disorder characterized by global developmental delay, variable neurologic features such as seizures, ataxia, and optic atrophy, dysmorphic facial features, distal skeletal anomalies, and combined immunodeficiency manifest as recurrent infections (summary by Sharfe et al., 2018).

Congenital tufting enteropathy (CTE) is a rare inherited intractable diarrhea of infancy characterized by villous atrophy and absence of inflammation, with intestinal epithelial cell dysplasia manifesting as focal epithelial tufts in the duodenum and jejunum. CTE presents in the first few months of life with chronic watery diarrhea and failure to thrive, and most affected individuals require parenteral nutrition for normal growth and development (summary by Sivagnanam et al., 2008). Semiquantitative assessment of the epithelial surface in CTE patients revealed that 80 to 90% contained tufts, compared to only 16% in patients with celiac disease and less than 10% in normal jejunum (Reifen et al., 1994). For a discussion of genetic heterogeneity of diarrhea, see DIAR1 (214700).

Lack of production of either functional C1r or C1s protein, due to a genetic defect. Approximately 60% of patients with a C1r/C1s deficiency will develop a severe systemic lupus erythematosus at an early age. Patients also present with frequent sinopulmonary infections often with Streptococcus pneumoniae.

Common variable immunodeficiency-8 with autoimmunity is an autosomal recessive disorder of immune dysregulation. Affected individuals have early childhood onset of recurrent infections, particularly respiratory infections, and also develop variable autoimmune disorders, including idiopathic thrombocytopenic purpura, autoimmune hemolytic anemia, and inflammatory bowel disease. The presentation and phenotype are highly variable, even within families (summary by Lopez-Herrera et al., 2012 and Alangari et al., 2012). Immunologic findings are also variable and may include decreased B cells, hypogammaglobulinemia, and deficiency of CD4+ T regulatory (Treg) cells (Charbonnier et al., 2015). For a general description and a discussion of genetic heterogeneity of common variable immunodeficiency, see CVID1 (607594).

Developmental dysplasia of the hip (DDH) is a debilitating condition characterized by incomplete formation of the acetabulum leading to dislocation of the femur, suboptimal joint function, and accelerated wear of the articular cartilage, resulting in arthritis. Undetected hip dysplasia is the leading cause of osteoarthritis of the hip in young individuals, causing over 40% of cases in that age group (summary by Feldman et al., 2013). For discussion of genetic heterogeneity of developmental dysplasia of the hip, see DDH1 (142700).

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.

Adenosine deaminase 2 deficiency (DADA2) is a complex systemic autoinflammatory disorder in which vasculopathy/vasculitis, dysregulated immune function, and/or hematologic abnormalities may predominate. Inflammatory features include intermittent fevers, rash (often livedo racemosa/reticularis), and musculoskeletal involvement (myalgia/arthralgia, arthritis, myositis). Vasculitis, which usually begins before age ten years, may manifest as early-onset ischemic (lacunar) and/or hemorrhagic strokes, or as cutaneous or systemic polyarteritis nodosa. Hypertension and hepatosplenomegaly are often found. More severe involvement may lead to progressive central neurologic deficits (dysarthria, ataxia, cranial nerve palsies, cognitive impairment) or to ischemic injury to the kidney, intestine, and/or digits. Dysregulation of immune function can lead to immunodeficiency or autoimmunity of varying severity; lymphadenopathy may be present and some affected individuals have had lymphoproliferative disease. Hematologic disorders may begin early in life or in late adulthood, and can include lymphopenia, neutropenia, pure red cell aplasia, thrombocytopenia, or pancytopenia. Of note, both interfamilial and intrafamilial phenotypic variability (e.g., in age of onset, frequency and severity of manifestations) can be observed; also, individuals with biallelic ADA2 pathogenic variants may remain asymptomatic until adulthood or may never develop clinical manifestations of DADA2.

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.

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.

Yao syndrome (YAOS) is an autoinflammatory disease characterized by periodic fever, dermatitis, arthritis, and swelling of the distal extremities, as well as gastrointestinal and sicca-like symptoms. The disorder is associated with specific NOD2 variants (and Shen, 2017).

DFNA34 is an autosomal dominant form of postlingual, slowly progressive sensorineural hearing loss with variable severity and variable additional features. Some patients have pure hearing loss without significant additional features, whereas some patients have features of an autoinflammatory disorder with systemic manifestations, including periodic fevers, arthralgias, and episodic urticaria. The disorder results from abnormally increased activation of the inflammatory pathway, and treatment with an IL1 receptor antagonist (see 147679) may be effective if started early (summary by Nakanishi et al., 2017).

Autosomal recessive primary hypertrophic osteoarthropathy-1 (PHOAR1) is a rare familial disorder characterized by digital clubbing, osteoarthropathy, and acroosteolysis, with variable features of pachydermia, delayed closure of the fontanels, and congenital heart disease (summary by Uppal et al., 2008; Radhakrishnan et al., 2020). Secondary hypertrophic osteoarthropathy, or pulmonary hypertrophic osteoarthropathy, is a different disorder characterized by digital clubbing secondary to acquired diseases, most commonly intrathoracic neoplasm (Uppal et al., 2008). Touraine et al. (1935) recognized pachydermoperiostosis as a familial disorder with 3 clinical presentations or forms: a complete form characterized by periostosis and pachydermia; an incomplete form with bone changes but without pachydermia; and a 'forme fruste' with pachydermia and minimal skeletal changes. Genetic Heterogeneity Autosomal recessive primary hypertrophic osteoarthropathy-2-enteropathy syndrome (PHOAR2E; 614441) is caused by mutation in the SLCO2A1 gene (601460) on chromosome 3q22. Families with an autosomal dominant form of primary hypertrophic osteoarthropathy have also been reported (PHOAD; 167100).

Cryopyrin-associated periodic syndromes (CAPS) are a group of conditions that have overlapping signs and symptoms and the same genetic cause. The group includes three conditions known as familial cold autoinflammatory syndrome type 1 (FCAS1), Muckle-Wells syndrome (MWS), and neonatal-onset multisystem inflammatory disorder (NOMID). These conditions were once thought to be distinct disorders but are now considered to be part of the same condition spectrum. FCAS1 is the least severe form of CAPS, MWS is intermediate in severity, and NOMID is the most severe form.\n\nThe signs and symptoms of CAPS affect multiple body systems. Generally, CAPS are characterized by periodic episodes of skin rash, fever, and joint pain. These episodes can be triggered by exposure to cold temperatures, fatigue, other stressors, or they may arise spontaneously. Episodes can last from a few hours to several days. These episodes typically begin in infancy or early childhood and persist throughout life.\n\nIn people with NOMID, the signs and symptoms of the condition are usually present from birth and persists throughout life. In addition to skin rash and fever, affected individuals may have joint inflammation, swelling, and joint deformities called contractures that may restrict movement. People with NOMID typically have headaches, seizures, and cognitive impairment resulting from chronic meningitis, which is inflammation of the tissue that covers and protects the brain and spinal cord (meninges). Other features of NOMID include eye problems, short stature, distinctive facial features, and kidney damage caused by amyloidosis.\n\nWhile the CAPS spectrum shares similar signs and symptoms, the individual conditions tend to have distinct patterns of features. People with FCAS1 are particularly sensitive to the cold, and exposure to cold temperatures can trigger a painful or burning rash. The rash usually affects the torso and limbs but may spread to the rest of the body. In addition to fever and joint pain, other possible symptoms include muscle aches, chills, drowsiness, eye redness, headache, and nausea.\n\nIndividuals with MWS develop the typical periodic episodes of skin rash, fever, and joint pain after cold exposure, although episodes may occur spontaneously or all the time. Additionally, they can develop progressive hearing loss in their teenage years. Other features of MWS include skin lesions or kidney damage from abnormal deposits of a protein called amyloid (amyloidosis).

Proteasome-associated autoinflammatory syndrome-3 is an autosomal recessive syndrome with onset in early infancy. Affected individuals present with nodular dermatitis, recurrent fever, myositis, panniculitis-induced lipodystrophy, lymphadenopathy, and dysregulation of the immune response, particularly associated with abnormal type I interferon-induced gene expression patterns. Additional features are highly variable, but may include joint contractures, hepatosplenomegaly, anemia, thrombocytopenia, recurrent infections, autoantibodies, and hypergammaglobulinemia. Some patients may have intracranial calcifications (summary by Brehm et al., 2015). For a discussion of genetic heterogeneity of PRAAS, see PRAAS1 (256040).

Blau syndrome is characterized by the triad of granulomatous arthritis, uveitis, and dermatitis. First described in 1985, it was considered to be distinct from sarcoidosis due to the early age of onset and autosomal dominant inheritance pattern. Published reports of sporadic cases of children with 'early-onset sarcoidosis' (EOS) with granulomatous involvement of different organs, primarily affecting joints, eyes, and skin, were suspected to represent the same disorder because the patients' characteristics were nearly identical. Subsequently, identical NOD2 mutations were identified in patients with Blau syndrome as well as in patients diagnosed with EOS, confirming earlier suspicions that they represented the same disease (summary by Borzutzky et al., 2010). Unlike older children diagnosed with sarcoidosis, these patients have no apparent pulmonary involvement; however, the disease is progressive and may result in severe complications such as blindness and/or joint destruction (Shetty and Gedalia, 1998).

Autoimmune interstitial lung, joint, and kidney disease is an autosomal dominant systemic autoimmune disorder characterized by interstitial lung disease, inflammatory arthritis, and immune complex-mediated renal disease. Laboratory studies show high-titer autoantibodies. Symptoms appear in the first 2 decades of life, but there is incomplete penetrance (summary by Watkin et al., 2015).

VEXAS (vacuoles, E1 enzyme, X-linked, autoinflammatory, somatic syndrome) is an adult-onset inflammatory disease that primarily affects males and is caused by somatic, not germline, mutations. The disorder is characterized by adult onset of rheumatologic symptoms at a mean age of 64 years. Features include recurrent fevers, pulmonary and dermatologic inflammatory manifestations, vasculitis, deep vein thrombosis, arthralgias, and ear and nose chondritis. Laboratory studies indicate hematologic abnormalities, including macrocytic anemia, as well as increased levels of acute-phase reactants; about half of patients have positive autoantibodies. Bone marrow biopsy shows degenerative vacuolization restricted to myeloid and erythroid precursor cells, as well as variable hematopoietic dyspoiesis and dysplasias. The condition does not respond to rheumatologic medications and the features may result in premature death (summary by Beck et al., 2020).

Immunodeficiency-82 with systemic inflammation (IMD82) is a complex autosomal dominant immunologic disorder characterized by recurrent infections with various organisms, as well as noninfectious inflammation manifest as lymphocytic organ infiltration with gastritis, colitis, and lung, liver, CNS, or skin disease. One of the more common features is inflammation of the stomach and bowel. Most patients develop symptoms in infancy or early childhood; the severity is variable. There may be accompanying fever, elevated white blood cell count, decreased B cells, hypogammaglobulinemia, increased C-reactive protein (CRP; 123260), and a generalized hyperinflammatory state. Immunologic workup shows variable B- and T-cell abnormalities such as skewed subgroups. Patients have a propensity for the development of lymphoma, usually in adulthood. At the molecular level, the disorder results from a gain-of-function mutation that leads to constitutive and enhanced activation of the intracellular inflammatory signaling pathway. Treatment with SYK inhibitors rescued human cell abnormalities and resulted in clinical improvement in mice (Wang et al., 2021).

Combined oxidative phosphorylation deficiency-53 (COXPD53) is an autosomal recessive disorder characterized by hypomyelination, microcephaly, liver dysfunction, and recurrent autoinflammation (summary by Lausberg et al., 2021). For a discussion of genetic heterogeneity of combined oxidative phosphorylation deficiency, see COXPD1 (609060).

X-linked familial Behcet-like autoinflammatory syndrome-2 (AIFBL2) is an X-linked recessive disorder characterized by the onset of inflammatory symptoms in the first decade of life in male patients. Affected males often present with oral mucosal ulceration and skin inflammation. More variable features may include gastrointestinal ulceration, arthritis, recurrent fevers, and iron deficiency anemia. Laboratory studies are consistent with immune dysregulation manifest as increased inflammatory markers and variable immune cell abnormalities, such as decreased NK cells and low memory B cells. One patient presented with recurrent infections and immunodeficiency in addition to autoinflammation. The disorder results from a defect in ELF4, which normally acts as a negative regulator of inflammatory disease. Symptoms may respond to blockade of IL1 (see 147760) or TNFA (191160) (summary by Tyler et al., 2021 and Sun et al., 2022). For a discussion of genetic heterogeneity of AIFBL, see AIFBL1 (616744).

Familial thoracic aortic aneurysm-12 (AAT12) is characterized by dilation of the arterial wall associated with a progressive loss of its ability to withstand the wall tension generated by high intraluminal pressure, which can lead to intramural or complete acute vessel wall rupture. Some patients have dolichostenomelia (summary by Elbitar et al., 2021). For a general phenotypic description and a discussion of genetic heterogeneity of thoracic aortic aneurysm, see AAT1 (607086).

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.