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.

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.

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.

Atopy is an allergic disorder characterized by immunoglobulin E (IgE) responses to environmental proteins that are otherwise innocuous and predominantly found in plant pollen and house dust. It is the major cause of asthma (see 600807), rhinitis (see 607154), and eczema (see 603165) in children and young adults (summary by Young et al., 1992).

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 group of rare autosomal recessive forms of ichthyosis with clinical characteristics of superficial, asymptomatic, spontaneous peeling of the skin and histologically by a shedding of the outer layers of the epidermis. Presents with either an acral or a generalised distribution.

Immunodeficiency-41 is an autosomal recessive complex disorder of immune dysregulation. Affected individuals present in infancy with recurrent viral, fungal, and bacterial infections, lymphadenopathy, and variable autoimmune features, such as autoimmune enteropathy and eczematous skin lesions. Immunologic studies show a defect in T-cell regulation (summary by Goudy et al., 2013).

Any severe combined immunodeficiency in which the cause of the disease is a mutation in the CD247 gene.

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.

Adenosine deaminase (ADA) deficiency is a systemic purine metabolic disorder that primarily affects lymphocyte development, viability, and function. The clinical phenotypic spectrum includes: Severe combined immunodeficiency disease (SCID), often diagnosed by age six months and usually by age 12 months; Less severe "delayed" onset combined immune deficiency (CID), usually diagnosed between age one and ten years; "Late/adult onset" CID, diagnosed in the second to fourth decades; Benign "partial ADA deficiency" (very low or absent ADA activity in erythrocytes but greater ADA activity in nucleated cells), which is compatible with normal immune function. Infants with typical early-onset ADA-deficient SCID have failure to thrive and opportunistic infections associated with marked depletion of T, B, and NK lymphocytes, and an absence of both humoral and cellular immune function. If immune function is not restored, children with ADA-deficient SCID rarely survive beyond age one to two years. Infections in delayed- and late-onset types (commonly, recurrent otitis, sinusitis, and upper respiratory) may initially be less severe than those in individuals with ADA-deficient SCID; however, by the time of diagnosis these individuals often have chronic pulmonary insufficiency and may have autoimmune phenomena (cytopenias, anti-thyroid antibodies), allergies, and elevated serum concentration of IgE. The longer the disorder goes unrecognized, the more immune function deteriorates and the more likely are chronic sequelae of recurrent infection.

Severe combined immunodeficiency (SCID) due to DCLRE1C deficiency is a type of SCID (see this term) characterized by severe and recurrent infections, diarrhea, failure to thrive, and cell sensitivity to ionizing radiation.

Immunodeficiency-35 (IMD35) is an autosomal recessive primary immunodeficiency characterized by increased susceptibility to localized or disseminated mycobacterial infection after BCG vaccination. Some patients may have increased susceptibility to infection with other intracellular organisms and/or viral infections. Fungal infections are not observed. Laboratory studies show normal levels of immune cells but defective signaling in specific immunologic pathways (summary by Kreins et al., 2015).

Any neonatal inflammatory skin and bowel disease in which the cause of the disease is a mutation in the ADAM17 gene.

A rare genetic epidermal disorder with characteristics of congenital erythroderma with severe psoriasiform dermatitis, ichthyosis, severe palmoplantar keratoderma, yellow keratosis on the hands and feet, elevated immunoglobulin E, multiple food allergies, and metabolic wasting. Other variable features may include hypotrichosis, nail dystrophy, recurrent infections, mild global developmental delay, eosinophilia, nystagmus, growth impairment and cardiac defects.

IMD23 is an autosomal recessive primary immunodeficiency syndrome characterized by onset of recurrent infections, usually respiratory or cutaneous, in early childhood. Immune workup usually shows neutropenia, lymphopenia, eosinophilia, and increased serum IgE or IgA. Neutrophil chemotactic defects have also been reported. Infectious agents include bacteria, viruses, and fungi. Many patients develop atopic dermatitis, eczema, and other signs of autoinflammation. Affected individuals may also show developmental delay or cognitive impairment of varying severity (summary by Bjorksten and Lundmark, 1976 and Zhang et al., 2014).

Neonatal nephrocutaneous inflammatory syndrome (NNCIS) is an autosomal recessive disorder characterized by intrauterine growth retardation and premature birth, fragile infection-prone skin, and nephromegaly with tubular dysfunction. Some patients have chronic diarrhea, and necrotizing enterocolitis with intestinal perforation has been observed. Other features include facial dysmorphisms and cardiac anomalies. Most patients require ventilatory and circulatory support at birth, exhibit failure to thrive, experience recurrent infections with sepsis as a common complication, and die within 6 months (Mazurova et al., 2020; Labbouz et al., 2023). Reviews Takeichi and Akiyama (2021) reviewed published reports of patients with mutation in the EGFR gene, whose features included intrauterine growth restriction; thin, translucent, and fragile skin (14 of 15 cases); skin desquamation (10 of 17 cases); ichthyosis (9 of 17 cases); recurrent skin infections and sepsis (9 of 12 cases); nephromegaly (10 of 16 cases); and congenital heart defects (7 of 17 cases). Other observed features included erythroderma, tubulopathy, necrotizing enterocolitis/intestinal perforation, cryptorchidism, hyperimmunoglobulin E, and dentinogenesis imperfecta. Almost all children died within 2.5 years after birth. The authors suggested that EGFR-associated systemic inflammatory diseases should be considered a part of the clinical spectrum of 'autoinflammatory keratinization diseases' (AiKDs).

LICS is an autosomal recessive chromosome breakage syndrome characterized by failure to thrive in infancy, immune deficiency, and fatal progressive pediatric lung disease induced by viral infection. Some patients may have mild dysmorphic features (summary by van der Crabben et al., 2016).

IMD11B is an autosomal dominant disorder of immune dysfunction characterized by onset of moderate to severe atopic dermatitis in early childhood. Some patients may have recurrent infections and other variable immune abnormalities. Laboratory studies show defects in T-cell activation, increased IgE, and eosinophilia (summary by Ma et al., 2017).

Hyper-IgE syndrome-2 with recurrent infections (HIES2) is an autosomal recessive immunologic disorder characterized by recurrent staphylococcal infections of the skin and respiratory tract, eczema, elevated serum immunoglobulin E, and hypereosinophilia. It is distinguished from autosomal dominant HIES1 (147060) by the lack of connective tissue and skeletal involvement (Renner et al., 2004). For a discussion of genetic heterogeneity of hyper-IgE syndrome, see 147060. See also TYK2 deficiency (611521), a clinically distinct disease entity that includes characteristic features of both autosomal recessive HIES2 and mendelian susceptibility to mycobacterial disease (MSMD; 209950) (Minegishi et al., 2006).

A rare genetic disease characterized by infantile onset of severe inflammatory bowel disease manifesting with bloody diarrhea and failure to thrive, and central nervous system disease with global developmental delay and regression, impaired speech, hypotonia, hyperreflexia, and epilepsy. Brain imaging shows global cerebral atrophy, thin corpus callosum, delayed myelination, and posterior leukoencephalopathy. Cases with recurrent infections and impaired T-cell responses to stimulation, as well as decreased T-cell subsets, have been reported.

Hyper-IgE syndrome-3 with recurrent infections (HIES3) is an autosomal recessive immunologic disorder characterized by childhood onset of atopic dermatitis, skin infections particularly with Staphylococcus aureus, recurrent sinopulmonary infections, and increased serum IgE and IgG. Patients are susceptible to bacterial and fungal infections, including chronic mucocutaneous candidiasis. Immunologic workup shows impaired differentiation of CD4+ T cells into T-helper 17 cells, decreased memory B cells, and often decreased NK cells (summary by Beziat et al., 2018). For a discussion of genetic heterogeneity of hyper-IgE syndrome, see HIES1 (147060).

Hyper-IgE syndrome-4B with recurrent infections (HIES4B) is an autosomal recessive immunologic disorder characterized by early childhood onset of recurrent infections and skeletal abnormalities, including craniosynostosis and scoliosis. Patients are mainly susceptible to bacterial infections that affect the respiratory tract, skin, and eye. Immunologic workup shows increased serum IgE, intermittent eosinophilia, and impaired IL6 (147620) and IL27 (608273) downstream signaling that affects the development and function of certain B- and T-cell populations, as well as the acute-phase response; IL11 (147681) signaling in fibroblasts is also affected (summary by Shahin et al., 2019). For a discussion of genetic heterogeneity of hyper-IgE syndrome, see HIES1 (147060).

Hyper-IgE syndrome-5 with recurrent infections (HEIS5) is an autosomal recessive immunologic disorder characterized by onset of recurrent sinopulmonary and deep skin infections in early childhood. The infections are mostly caused by bacteria, including H. influenza and Staphylococcus aureus. Additional features include atopic dermatitis, impaired inflammatory responses during infection, increased serum IgE, and increased IL6 (147620) (summary by Spencer et al., 2019). For a discussion of genetic heterogeneity of hyper-IgE syndrome, see HIES1 (147060).

Immunodeficiency-72 with autoinflammation and lymphoproliferation (IMD72) is an autosomal recessive immunologic disorder characterized by onset of recurrent infections or systemic inflammation in the first year of life. Affected individuals develop bacterial and viral infections that can be severe, including bacteremia, recurrent pneumonia, and meningitis, consistent with an immunodeficiency. There is also an autoimmune and hyperinflammatory aspect to the disorder, manifest as atopy or allergies, hepatosplenomegaly, and lymphoproliferation, including hemophagocytic lymphohistiocytosis (HLH). Immunologic workup shows variable abnormalities, including low or high Ig subsets, increased B cells, irregular T-cell activation and cytokine response, impaired immune synapse formation, and defective cellular migration. At the cellular level, these defects are related to abnormal F-actin polymerization and altered intracellular signaling (summary by Cook et al., 2020).

Autosomal dominant growth hormone insensitivity syndrome with immune dysregulation-2 (GHISID2) is a congenital disorder characterized by short stature due to insensitivity to growth hormone (GH1; 139250). Affected individuals usually have delayed bone age, delayed puberty, and decreased serum IGF1 (147440). Some patients may have features of mild immune dysregulation, such as eczema, increased serum IgE, asthma, or celiac disease (summary by Klammt et al., 2018).

VISS syndrome is a generalized connective tissue disorder characterized by early-onset thoracic aortic aneurysm and other connective tissue findings, such as aneurysm and tortuosity of other arteries, joint hypermobility, skin laxity, and hernias, as well as craniofacial dysmorphic features, structural cardiac defects, skeletal anomalies, and motor developmental delay (Van Gucht et al., 2021). Immune dysregulation has been observed in some patients (Ziegler et al., 2021).

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).

A rare autosomal recessive primary immunodeficiency characterized by infancy onset of severe inflammatory bowel disease with life-threatening diarrhea and failure to thrive, oral aphthous ulcers, and recurrent severe upper and lower respiratory tract infections with finger clubbing. Laboratory examination reveals increased IgE and decreased IgG levels, as well as reduced numbers of circulating CD19+ B-cells including IgM+ naive and class-switched IgG memory B-cells, with a concomitant increase in transitional B-cells, while T-cell numbers and function are normal.

Netherton syndrome (NETH) is a rare and severe autosomal recessive skin disorder characterized by congenital erythroderma, a specific hair-shaft abnormality, and atopic manifestations with high IgE levels. Generalized scaly erythroderma is apparent at or soon after birth and usually persists. Scalp hair is sparse and brittle with a characteristic 'bamboo' shape under light microscopic examination due to invagination of the distal part of the hair shaft to its proximal part. Atopic manifestations include eczema-like rashes, atopic dermatitis, pruritus, hay fever, angioedema, urticaria, high levels of IgE in the serum, and hypereosinophilia. Life-threatening complications are frequent during the neonatal period, including hypernatremic dehydration, hypothermia, extreme weight loss, bronchopneumonia, and sepsis. During childhood, failure to thrive is common as a result of malnutrition, metabolic disorders, chronic erythroderma, persistent cutaneous infections, or enteropathy (summary by Bitoun et al., 2002).

Hyper-IgE syndrome-4A with recurrent infections (HIES4A) is an autosomal dominant immunologic disorder characterized by recurrent, mainly sinopulmonary infections associated with increased serum IgE. The phenotype is variable, even within families. Some patients have onset of symptoms in early childhood and develop complications, including bronchiectasis or hemoptysis, whereas others have later onset of less severe infections. Immunologic workup usually shows normal leukocyte levels, although some patients may demonstrate alterations in lymphocyte subsets, including T cells. Affected individuals also have variable skeletal abnormalities, including high-arched palate, hyperextensible joints, scoliosis, and bone fractures. The IL6ST mutations are loss-of-function, although the truncated mutant proteins are expressed and interfere with the wildtype protein in a dominant-negative manner by disrupting IL6 (147620) and IL11 (147681) signaling (summary by Beziat et al., 2020). For a discussion of genetic heterogeneity of hyper-IgE syndrome, see HIES1 (147060).

X-linked multisystem autoinflammatory disease with immune dysregulation (ADMIDX) is an X-linked recessive disorder with onset of symptoms in infancy or early childhood. Affected individuals may present with variable cytopenias, including anemia, thrombocytopenia, neutropenia, lymphopenia, or hypogammaglobulinemia, and systemic or organ-specific autoinflammatory manifestations. These include skin lesions, panniculitis, inflammatory bowel disease, pulmonary disease, or arthritis associated with recurrent fever, leukocytosis, lymphoproliferation, and hepatosplenomegaly in the absence of an infectious agent. Some patients have circulating autoantibodies that underlie the cytopenias or systemic features, whereas others do not have circulating autoantibodies. In addition, some patients have recurrent infections, whereas others do not show signs of an immunodeficiency. Laboratory studies are consistent with immune dysregulation, including altered B-cell subsets and variably elevated proinflammatory cytokines. Detailed functional studies of platelets, red cells, and T lymphocytes suggest that abnormal actin cytoskeleton remodeling is a basic defect, indicating that this disorder can be classified as an immune-related actinopathy. Severe complications of the disease may result in death in childhood (Boussard et al., 2023; Block et al., 2023).

Hyper-IgE syndrome-6 with recurrent infections (HIES6) is an autosomal dominant immunologic disorder characterized by early-childhood onset of severe refractory atopic dermatitis, IgE-mediated food and drug allergies, asthma, and eosinophilic esophagitis. Laboratory studies show increased serum IgE levels and eosinophilia. Affected individuals are susceptible to life-threatening anaphylaxis. Additional features may include allergic rhinitis, recurrent secondary infections (bacterial, viral, fungal), and short stature. Rare patients show intracerebral vascular abnormalities, including the Circle of Willis, increased risk of ruptured aneurysm, and B-cell lymphoma. The disorder results from immune dysregulation with inappropriate activation of inflammatory signaling pathways associated with a Th2 phenotype. Treatment with an IL4 (147780)/IL13 (147683) inhibitor (dupilumab) or JAK inhibitor results in clinical improvement. Sharma et al. (2023) classified this disease as a 'primary atopic disorder' (PAD). For a discussion of genetic heterogeneity of hyper-IgE syndrome, see HIES1 (147060).

Immunodeficiency-113 with autoimmunity and autoinflammation (IMD113) is an autosomal recessive complex immunologic disorder with onset of symptoms in infancy. Affected individuals have recurrent infections and usually show features of autoimmunity and autoinflammation, such as hemolytic anemia, thrombocytopenia, hepatosplenomegaly, leukocytosis, neutrophilia, and elevated acute phase reactants. More variable systemic features may include celiac disease or enteropathy, ileus, nephropathy, eczema, and dermatomyositis. Additional features include facial dysmorphism, scoliosis, and poor wound healing. One patient with neurodevelopmental abnormalities has been reported. The disorder results from dysregulation of the actin cytoskeleton that affects certain cell lineages (Nunes-Santos et al., 2023).

Folate-responsive immunodeficiency-114 (IMD114) is an autosomal recessive immunologic disorder characterized by the onset of oral ulcers and recurrent skin and respiratory infections in early infancy. Affected individuals have lip fissures, skin sores and abscesses, genital dermatitis, chronic diarrhea, and poor overall growth. Laboratory studies show megaloblastic anemia, thrombocytopenia, and lymphopenia with decreased Ig levels. Some individuals have global developmental delay, often with brain imaging abnormalities. Treatment with folic acid supplementation results in significant clinical improvement of the hematologic and immunologic abnormalities, although neurologic abnormalities, if already present, do not respond to treatment. Early intervention and treatment with folic acid supplementation may prevent or delay neurologic deficits in affected infants (Gok et al., 2023; Shiraishi et al., 2023).

STAT3 hyper IgE syndrome (STAT3-HIES) is a primary immune deficiency syndrome characterized by elevated serum IgE, eczema, and recurrent skin and respiratory tract infections, together with several nonimmune features. This disorder typically manifests in the newborn period with a rash (often diagnosed as eosinophilic pustulosis) that subsequently evolves into an eczematoid dermatitis. Recurrent staphylococcal skin boils and bacterial pneumonias usually manifest in the first years of life. Pneumatoceles and bronchiectasis often result from aberrant healing of pneumonias. Mucocutaneous candidiasis is common. Nonimmune features may include retained primary teeth, scoliosis, bone fractures following minimal trauma, joint hyperextensibility, and characteristic facial appearance, which typically emerges in adolescence. Vascular abnormalities have been described and include middle-sized artery tortuosity and aneurysms, with infrequent clinical sequelae of myocardial infarction and subarachnoid hemorrhage. Gastrointestinal (GI) manifestations include gastroesophageal reflux disease, esophageal dysmotility, and spontaneous intestinal perforations (some of which are associated with diverticuli). Fungal infections of the GI tract (typically histoplasmosis, Cryptococcus, and Coccidioides) also occur infrequently. Survival is typically into adulthood, with most individuals now living into or past the sixth decade. Most deaths are associated with gram-negative (Pseudomonas) or filamentous fungal pneumonias resulting in hemoptysis. Lymphomas occur at an increased frequency.

Epidermolytic palmoplantar keratoderma-1 (EPPK1) is an autosomal dominant skin disorder characterized clinically by diffuse, yellow thickening of the skin of the palms and soles. There is no extension of the keratoderma to dorsal surfaces of hands and feet, inner wrists, and Achilles tendon area (transgrediens). Knuckle pads may be present in some individuals (summary by Kuster et al., 2002, Chiu et al., 2007). Genetic Heterogeneity of Epidermolytic Palmoplantar Keratoderma Epidermolytic palmoplantar keratoderma-2 (EPPK2; 620411) is caused by mutation in the keratin-1 gene (KRT1; 139350) on chromosome 12q13. Classification of Palmoplantar Keratoderma PPK has been classified into diffuse, focal, and punctate forms according to the pattern of hyperkeratosis on the palms and soles (Lucker et al., 1994). Diffuse PPK develops at birth or shortly thereafter and involves the entire palm and sole with a sharp cutoff at an erythematous border; there are no lesions outside the volar skin, and, in particular, no follicular or oral lesions. In contrast, focal PPK is a late-onset form in which focal hyperkeratotic lesions develop in response to mechanical trauma; an important distinguishing feature is the presence of lesions at other body sites, e.g., oral and follicular hyperkeratosis (Stevens et al., 1996). Palmoplantar keratodermas can be further subdivided histologically into epidermolytic and nonepidermolytic PPK (Risk et al., 1994). Genetic Heterogeneity of Palmoplantar Keratoderma Nonepidermolytic palmoplantar keratoderma (NEPPK; 600962) is caused by mutation in the KRT1 gene. A focal form of NEPPK (FNEPPK1; 613000) is caused by mutation in the KRT16 gene (148067). Another focal form, FNEPPK2 (616400), is caused by mutation in the TRPV3 gene (607066); mutation in TRPV3 can also cause Olmsted syndrome (OLMS; 614594), a severe mutilating form of PPK. The diffuse Bothnian form of NEPPK (PPKB; 600231) is caused by mutation in the AQP5 gene (600442). The Nagashima type of nonepidermolytic diffuse PPK (PPKN; 615598) is caused by mutation in the SERPINB7 gene (603357). A generalized form of epidermolytic hyperkeratosis (EHK; 113800), also designated bullous congenital ichthyosiform erythroderma (BCIE), is caused by mutation in the keratin genes KRT1 and KRT10 (148080). For a discussion of punctate PPK, see 148600; for a discussion of striate PPK, see 148700.