Peutz-Jeghers syndrome (PJS) is characterized by the association of gastrointestinal (GI) polyposis, mucocutaneous pigmentation, and cancer predisposition. PJS-type hamartomatous polyps are most common in the small intestine (in order of prevalence: jejunum, ileum, and duodenum) but can also occur in the stomach, large bowel, and extraintestinal sites including the renal pelvis, bronchus, gall bladder, nasal passages, urinary bladder, and ureters. GI polyps can result in chronic bleeding, anemia, and recurrent obstruction and intussusception requiring repeated laparotomy and bowel resection. Mucocutaneous hyperpigmentation presents in childhood as dark blue to dark brown macules around the mouth, eyes, and nostrils, in the perianal area, and on the buccal mucosa. Hyperpigmented macules on the fingers are common. The macules may fade in puberty and adulthood. Recognition of the distinctive skin manifestations is important especially in individuals who have PJS as the result of a de novo pathogenic variant as these skin findings often predate GI signs and symptoms. Individuals with PJS are at increased risk for a wide variety of epithelial malignancies (colorectal, gastric, pancreatic, breast, and ovarian cancers). Females are at risk for sex cord tumors with annular tubules (SCTAT), a benign neoplasm of the ovaries, and adenoma malignum of the cervix, a rare aggressive cancer. Males occasionally develop large calcifying Sertoli cell tumors of the testes, which secrete estrogen and can lead to gynecomastia, advanced skeletal age, and ultimately short stature, if untreated.

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).

Lymphocytic interstitial pneumonitis is a benign lymphoproliferative disorder of the lung that is characterized by the presence of a dense, predominantly lymphocytic interstitial infiltrate (lymphocytes, plasma cells, other elements of the lymphoreticular system) that expands the alveolar septa.

The FLNB disorders include a spectrum of phenotypes ranging from mild to severe. At the mild end are spondylocarpotarsal synostosis (SCT) syndrome and Larsen syndrome; at the severe end are the phenotypic continuum of atelosteogenesis types I (AOI) and III (AOIII) and Piepkorn osteochondrodysplasia (POCD). SCT syndrome is characterized by postnatal disproportionate short stature, scoliosis and lordosis, clubfeet, hearing loss, dental enamel hypoplasia, carpal and tarsal synostosis, and vertebral fusions. Larsen syndrome is characterized by congenital dislocations of the hip, knee, and elbow; clubfeet (equinovarus or equinovalgus foot deformities); scoliosis and cervical kyphosis, which can be associated with a cervical myelopathy; short, broad, spatulate distal phalanges; distinctive craniofacies (prominent forehead, depressed nasal bridge, malar flattening, and widely spaced eyes); vertebral anomalies; and supernumerary carpal and tarsal bone ossification centers. Individuals with SCT syndrome and Larsen syndrome can have midline cleft palate and hearing loss. AOI and AOIII are characterized by severe short-limbed dwarfism; dislocated hips, knees, and elbows; and clubfeet. AOI is lethal in the perinatal period. In individuals with AOIII, survival beyond the neonatal period is possible with intensive and invasive respiratory support. Piepkorn osteochondrodysplasia (POCD) is a perinatal-lethal micromelic dwarfism characterized by flipper-like limbs (polysyndactyly with complete syndactyly of all fingers and toes, hypoplastic or absent first digits, and duplicated intermediate and distal phalanges), macrobrachycephaly, prominant forehead, hypertelorism, and exophthalmos. Occasional features include cleft palate, omphalocele, and cardiac and genitourinary anomalies. The radiographic features at mid-gestation are characteristic.

Cronkhite-Canada syndrome is characterized by gastrointestinal hamartomatous polyposis, alopecia, onychodystrophy, skin hyperpigmentation, and diarrhea. It is associated with high morbidity (summary by Sweetser et al., 2012).

A rare genetic skin disease characterized by generalized poikiloderma with marked accentuation in flexural regions and on extensor surfaces, sclerosis of palms and soles, and linear and reticulated hyperkeratotic and sclerotic bands in the axilla and the antecubital and popliteal fossae. Subcutaneous calcification, finger clubbing, Raynaud phenomenon, and cardiac abnormalities (such as severe aortic stenosis) have also been reported.

Digital clubbing is characterized by enlargement of the nail plate and terminal segments of the fingers and toes, resulting from proliferation of the connective tissues between the nail matrix and the distal phalanx (Myers and Farquhar, 2001).

Juvenile polyposis syndrome (JPS) is characterized by predisposition to hamartomatous polyps in the gastrointestinal (GI) tract, specifically in the stomach, small intestine, colon, and rectum. The term "juvenile" refers to the type of polyp rather than to the age of onset of polyps. Most individuals with JPS have some polyps by age 20 years; some may have only four or five polyps over their lifetime, whereas others in the same family may have more than 100. If the polyps are left untreated, they may cause bleeding and anemia. Most juvenile polyps are benign; however, malignant transformation can occur. Risk for GI cancers ranges from 11% to 86%. Most of this increased risk is attributed to colon cancer, but cancers of the stomach, upper GI tract, and pancreas have also been reported. A combined syndrome of JPS and hereditary hemorrhagic telangiectasia (HHT) is present in most individuals with an SMAD4 pathogenic variant.

Autosomal recessive congenital ichthyosis (ARCI) encompasses several forms of nonsyndromic ichthyosis. Although most neonates with ARCI are collodion babies, the clinical presentation and severity of ARCI may vary significantly, ranging from harlequin ichthyosis, the most severe and often fatal form, to lamellar ichthyosis (LI) and (nonbullous) congenital ichthyosiform erythroderma (CIE). These phenotypes are now recognized to fall on a continuum; however, the phenotypic descriptions are clinically useful for clarification of prognosis and management. Infants with harlequin ichthyosis are usually born prematurely and are encased in thick, hard, armor-like plates of cornified skin that severely restrict movement. Life-threatening complications in the immediate postnatal period include respiratory distress, feeding problems, and systemic infection. Collodion babies are born with a taut, shiny, translucent or opaque membrane that encases the entire body and lasts for days to weeks. LI and CIE are seemingly distinct phenotypes: classic, severe LI with dark brown, plate-like scale with no erythroderma and CIE with finer whiter scale and underlying generalized redness of the skin. Affected individuals with severe involvement can have ectropion, eclabium, scarring alopecia involving the scalp and eyebrows, and palmar and plantar keratoderma. Besides these major forms of nonsyndromic ichthyosis, a few rare subtypes have been recognized, such as bathing suit ichthyosis, self-improving collodion ichthyosis, or ichthyosis-prematurity syndrome.

Hereditary hemorrhagic telangiectasia (HHT) is characterized by the presence of multiple arteriovenous malformations (AVMs) that lack intervening capillaries and result in direct connections between arteries and veins. The most common clinical manifestation is spontaneous and recurrent nosebleeds (epistaxis) beginning on average at age 12 years. Telangiectases (small AVMs) are characteristically found on the lips, tongue, buccal and gastrointestinal (GI) mucosa, face, and fingers. The appearance of telangiectases is generally later than epistaxis but may be during childhood. Large AVMs occur most often in the lungs, liver, or brain; complications from bleeding or shunting may be sudden and catastrophic. A minority of individuals with HHT have GI bleeding, which is rarely seen before age 50 years.

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.

A rare genetic disorder characterised by split-hand/split-foot malformation (SHFM), facial anomalies, cleft lip/palate, congenital heart defect (CHD), genital anomalies, and intellectual deficit.

Hereditary hemorrhagic telangiectasia (HHT) is characterized by the presence of multiple arteriovenous malformations (AVMs) that lack intervening capillaries and result in direct connections between arteries and veins. The most common clinical manifestation is spontaneous and recurrent nosebleeds (epistaxis) beginning on average at age 12 years. Telangiectases (small AVMs) are characteristically found on the lips, tongue, buccal and gastrointestinal (GI) mucosa, face, and fingers. The appearance of telangiectases is generally later than epistaxis but may be during childhood. Large AVMs occur most often in the lungs, liver, or brain; complications from bleeding or shunting may be sudden and catastrophic. A minority of individuals with HHT have GI bleeding, which is rarely seen before age 50 years.

X-linked reticulate pigmentary disorder shows more severe manifestations in hemizygous males compared to heterozygous females. Affected males have early onset of recurrent respiratory infections and failure to thrive resulting from inflammatory gastroenteritis or colitis. Patients also show reticular pigmentation abnormalities of the skin and may develop corneal scarring. Carrier females may be unaffected or have only pigmentary abnormalities along the lines of Blaschko (summary by Starokadomskyy et al., 2016).

Isolated congenital adermatoglyphia is a rare, genetic developmental defect during embryogenesis disorder characterized by the lack of epidermal ridges on the palms and soles, resulting in the absence of fingerprints, with no other associated manifestations. It is associated with a reduced number of sweat gland openings and reduced transpiration of palms and soles.

Inborn errors of pulmonary surfactant metabolism are genetically heterogeneous disorders resulting in severe respiratory insufficiency or failure in full-term neonates or infants. These disorders are associated with various pathologic entities, including pulmonary alveolar proteinosis (PAP), desquamative interstitial pneumonitis (DIP), or cellular nonspecific interstitial pneumonitis (NSIP) (Clark and Clark, 2005). A clinically similar disorder characterized by respiratory distress (267450) can affect preterm infants, who show developmental deficiency of surfactant. Acquired PAP (610910) is an autoimmune disorder characterized by the presence of autoantibodies to CSF2 (138960). Genetic Heterogeneity of Pulmonary Surfactant Metabolism Dysfunction See also SMDP2 (610913), caused by mutation in the SPTPC gene (178620) on 8p21; SMDP3 (610921), caused by mutation in the ABCA3 gene (601615) on 16p13; SMDP4 (300770), caused by mutation in the CSF2RA gene (306250) on Xp22; and SMDP5 (614370), caused by mutation in the CSF2RB gene (138981) on 22q12.

Pitt-Hopkins syndrome (PTHS) is characterized by significant developmental delays with moderate-to-severe intellectual disability and behavioral differences, characteristic facial features, and episodic hyperventilation and/or breath-holding while awake. Speech is significantly delayed and most individuals are nonverbal with receptive language often stronger than expressive language. Other common findings are autism spectrum disorder symptoms, sleep disturbance, stereotypic hand movements, seizures, constipation, and severe myopia.

For a general phenotypic description and a discussion of genetic heterogeneity of pulmonary surfactant metabolism dysfunction, see SMDP1 (265120).

Pulmonary surfactant metabolism dysfunction-2 (SMDP2) is a rare autosomal dominant disease associated with progressive respiratory insufficiency and lung disease with a variable clinical course. The pathophysiology of the disorder is postulated to involve intracellular accumulation of a structurally defective SPC protein (Thomas et al., 2002). For a general phenotypic description and a discussion of genetic heterogeneity of pulmonary surfactant metabolism dysfunction, see SMDP1 (265120).

Pulmonary alveolar proteinosis is a pathologic entity characterized by intraalveolar surfactant accumulation. There are 3 clinically distinct forms: hereditary (usually congenital), secondary, and acquired. The acquired form of pulmonary alveolar proteinosis is the most common form, accounting for approximately 90% of cases. The mean age at diagnosis is 39 years and it is associated with smoking in 72% of cases. The estimated incidence and prevalence are 0.36 and 3.70 cases per million, respectively (Trapnell et al., 2003; Seymour and Presneill, 2002). Secondary pulmonary alveolar proteinosis develops in association with conditions involving functional impairment or reduced numbers of alveolar macrophages. Such conditions include some hematologic cancers, pharmacologic immunosuppression, inhalation of inorganic dust or toxic fumes, and certain infections. Congenital pulmonary alveolar proteinosis is a rare, severe, often fatal disorder of newborns associated with pulmonary surfactant metabolism dysfunction caused by mutations in genes involved in surfactant metabolism (see, e.g., SMDP1, 265120) (Trapnell et al., 2003). See 300770 for information on congenital PAP due to CSF2RA (306250) deficiency.

Any sarcoidosis in which the cause of the disease is a mutation in the BTNL2 gene.

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

Autosomal recessive primary hypertrophic osteoarthropathy-2 (PHOAR2) is a rare disorder characterized by digital clubbing, pachydermia, and periostosis. Pain and swelling of ankles and knees, watery diarrhea, and excessive sweating are often present. Males are more frequently and severely affected (summary by Zhang et al., 2013, Li et al., 2017). For a discussion of genetic heterogeneity of PHO, see PHOAR1 (259100).

Ichthyosis with confetti (IWC), also known as congenital reticular ichthyosiform erythroderma (CRIE), is a rare skin condition characterized by slowly enlarging islands of normal skin surrounded by erythematous ichthyotic patches in a reticulated pattern. The condition starts in infancy as a lamellar ichthyosis, with small islands of normal skin resembling confetti appearing in late childhood and at puberty. Histopathologic findings include band-like parakeratosis, psoriasiform acanthosis, and vacuolization of keratinocytes with binucleated cells in the upper epidermis, sometimes associated with amyloid deposition in the dermis. Ultrastructural abnormalities include perinuclear shells formed from a network of fine filaments in the upper epidermis (summary by Krunic et al., 2003).

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.

Interstitial lung and liver disease is an autosomal recessive disorder characterized by onset of respiratory insufficiency and progressive liver disease in infancy or early childhood. Pathologic examination of lung lavage is consistent with pulmonary alveolar proteinosis (summary by Hadchouel et al., 2015).

MPSPS is an autosomal recessive inborn error of metabolism resulting in a multisystem disorder with features of the mucopolysaccharidosis lysosomal storage diseases (see, e.g., 607016). Patients present in infancy or early childhood with respiratory difficulties, cardiac problems, anemia, dysostosis multiplex, renal involvement, coarse facies, and delayed psychomotor development. Most patients die of cardiorespiratory failure in the first years of life (summary by Kondo et al., 2017).

Any Meier-Gorlin syndrome in which the cause of the disease is a mutation in the CDC45 gene.

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 PHOAR2 (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).

Hereditary hemorrhagic telangiectasia (HHT) is characterized by the presence of multiple arteriovenous malformations (AVMs) that lack intervening capillaries and result in direct connections between arteries and veins. The most common clinical manifestation is spontaneous and recurrent nosebleeds (epistaxis) beginning on average at age 12 years. Telangiectases (small AVMs) are characteristically found on the lips, tongue, buccal and gastrointestinal (GI) mucosa, face, and fingers. The appearance of telangiectases is generally later than epistaxis but may be during childhood. Large AVMs occur most often in the lungs, liver, or brain; complications from bleeding or shunting may be sudden and catastrophic. A minority of individuals with HHT have GI bleeding, which is rarely seen before age 50 years.

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).

Pontocerebellar hypoplasia type 13 (PCH13) is an autosomal recessive disorder characterized by global developmental delay, impaired intellectual development with absent speech, microcephaly, and progressive atrophy of the cerebellar vermis and brainstem. Additional features, including seizures and visual impairment, are variable (summary by Uwineza et al., 2019). For a general phenotypic description and a discussion of genetic heterogeneity of PCH, see PCH1A (607596).

Cardioacrofacial dysplasia-2 (CAFD2) is characterized by congenital cardiac defects, primarily common atrium or atrioventricular septal defect; limb anomalies, including short limbs, brachydactyly, and postaxial polydactyly; and dysmorphic facial features. Developmental delay of variable severity has also been observed (Palencia-Campos et al., 2020). For a discussion of genetic heterogeneity of CAFD, see CAFD1 (619142).

Interstitial lung disease (ILD) comprises a heterogeneous group of rare diseases affecting the distal part of the lung and characterized by a progressive remodeling of the alveolar interstitium. The manifestations form a spectrum ranging from idiopathic interstitial pneumonia (IIP) or pneumonitis to the more severe idiopathic pulmonary fibrosis (IPF). IPF is associated with an increased risk of developing lung cancer, which occurs in a subset of patients with ILD. Clinical features of ILD include dyspnea, clubbing of the fingers, and restrictive lung capacity. Imaging typically shows ground glass opacities and inter- and intraseptal thickening, while histologic studies usually show a pattern consistent with 'usual interstitial pneumonia' (UIP) (summary by Nathan et al., 2016, Doubkova et al., 2019). Genetic Heterogeneity of Interstitial Lung Disease See also ILD2 (178500), caused by mutation in the SFTPA2 gene (178642) on chromosome 10q22.

Stuve-Wiedemann syndrome is an autosomal recessive disorder characterized by bowing of the long bones and other skeletal anomalies, episodic hyperthermia, respiratory distress, and feeding difficulties usually resulting in early death (Dagoneau et al., 2004). See also 'classic' Schwartz-Jampel syndrome type 1 (SJS1; 255800), a phenotypically similar but genetically distinct disorder caused by mutation in the HSPG2 gene (142461) on chromosome 1p36. Genetic Heterogeneity of Stuve-Wiedemann Syndrome Stuve-Wiedemann syndrome-2 (STWS2; 619751) is caused by mutation in the IL6ST gene (600694) on chromosome 5q11.