Individuals with 22q11.2 deletion syndrome (22q11.2DS) can present with a wide range of features that are highly variable, even within families. The major clinical manifestations of 22q11.2DS include congenital heart disease, particularly conotruncal malformations (ventricular septal defect, tetralogy of Fallot, interrupted aortic arch, and truncus arteriosus), palatal abnormalities (velopharyngeal incompetence, submucosal cleft palate, bifid uvula, and cleft palate), immune deficiency, characteristic facial features, and learning difficulties. Hearing loss can be sensorineural and/or conductive. Laryngotracheoesophageal, gastrointestinal, ophthalmologic, central nervous system, skeletal, and genitourinary anomalies also occur. Psychiatric illness and autoimmune disorders are more common in individuals with 22q11.2DS.

A multifocal, multisystem form of Langerhans-cell histiocytosis. There is involvement of multiple organ systems including the bones, skin, liver, spleen, and lymph nodes. Patients are usually infants presenting with fever, hepatosplenomegaly, lymphadenopathy, bone and skin lesions, and pancytopenia.

Thrombocytopenia absent radius (TAR) syndrome is characterized by bilateral absence of the radii with the presence of both thumbs, and thrombocytopenia that is generally transient. Thrombocytopenia may be congenital or may develop within the first few weeks to months of life; in general, thrombocytopenic episodes decrease with age. Cow's milk allergy is common and can be associated with exacerbation of thrombocytopenia. Other anomalies of the skeleton (upper and lower limbs, ribs, and vertebrae), heart, and genitourinary system (renal anomalies and agenesis of uterus, cervix, and upper part of the vagina) can occur.

If untreated, young children with profound biotinidase deficiency usually exhibit neurologic abnormalities including seizures, hypotonia, ataxia, developmental delay, vision problems, hearing loss, and cutaneous abnormalities (e.g., alopecia, skin rash, candidiasis). Older children and adolescents with profound biotinidase deficiency often exhibit motor limb weakness, spastic paresis, and decreased visual acuity. Once vision problems, hearing loss, and developmental delay occur, they are usually irreversible, even with biotin therapy. Individuals with partial biotinidase deficiency may have hypotonia, skin rash, and hair loss, particularly during times of stress.

A rare disorder of mineral absorption and transport characterized by hypocupremia that manifests as failure to thrive, mild anemia, repeated seizures, hypotonia and seborrheic skin. Spurring of the femur and tibia are also noted on radiographic imaging. Symptoms are reversible or improve with supplements of oral copper. There have been no further descriptions in the literature since 1982.

A rare genetic epidermal disorder with characteristics of a chronic diffuse fine scaly erythematous rash on the face (predominantly the chin, nasolabial folds, eyebrows) around the earlobes and over the scalp, associated with hyperkeratosis over elbows, knees, palms, soles and metacarpophalangeal joints, in the absence of associated rheumatological or neurological disorders. Cold weather, emotional stress and strenuous physical activity may exacerbate symptoms. There is evidence the disease is caused by mutation in the ZNF750 gene.

Infants with 3-MCC deficiency appear normal at birth but usually develop signs and symptoms in infancy or early childhood. The characteristic features of this condition, which can range from mild to life-threatening, include feeding difficulties, recurrent episodes of vomiting and diarrhea, excessive tiredness (lethargy), and weak muscle tone (hypotonia). If untreated, this disorder can lead to delayed development, seizures, and coma. Many of these complications can be prevented with early detection and lifelong management with a low-protein diet and appropriate supplements. Some people with gene mutations that cause 3-MCC deficiency never experience any signs or symptoms of the condition.\n\nThe characteristic features of 3-MCC deficiency are similar to those of Reye syndrome, a severe disorder that develops in children while they appear to be recovering from viral infections such as chicken pox or flu. Most cases of Reye syndrome are associated with the use of aspirin during these viral infections.\n\n3-methylcrotonyl-CoA carboxylase deficiency (also known as 3-MCC deficiency) is an inherited disorder in which the body is unable to process certain proteins properly. People with this disorder have a shortage of an enzyme that helps break down proteins containing a particular building block (amino acid) called leucine.

A rare syndrome comprising hypocalcified-hypoplastic tooth enamel, onycholysis with subungual hyperkeratosis, and hypohidrosis.

Autosomal dominant primary hypertrophic osteoarthropathy (PHOAD) is characterized by 3 major features: digital clubbing, periostosis, and pachydermia. Patients may also experience joint swelling and pain, and some have reported gastrointestinal symptoms, including watery diarrhea. Males are more commonly affected, and more severely affected, than females (Lee et al., 2016; Xu et al., 2021). Touraine et al. (1935) recognized pachydermoperiostosis (PDP) as a familial disorder with 3 presentations or forms: a complete form with periostosis and pachydermia, an incomplete form without pachydermia, and a forme fruste with pachydermia and minimal skeletal changes. Genetic Heterogeneity Autosomal recessive forms of PHO have been reported (see 259100), including PHOAR2 (614441), which is also caused by mutation in the SLCO2A1 gene.

Multiple congenital anomalies-hypotonia-seizures syndrome-2 (MCAHS2) is an X-linked recessive neurodevelopmental disorder characterized by dysmorphic features, neonatal hypotonia, early-onset myoclonic seizures, and variable congenital anomalies involving the central nervous, cardiac, and urinary systems. Some affected individuals die in infancy (summary by Johnston et al., 2012). The phenotype shows clinical variability with regard to severity and extraneurologic features. However, most patients present in infancy with early-onset epileptic encephalopathy associated with developmental arrest and subsequent severe neurologic disability; these features are consistent with a form of developmental and epileptic encephalopathy (DEE) (summary by Belet et al., 2014, Kato et al., 2014). The disorder is caused by a defect in glycosylphosphatidylinositol (GPI) biosynthesis. For a discussion of genetic heterogeneity of MCAHS, see MCAHS1 (614080). For a discussion of nomenclature and genetic heterogeneity of DEE, see 308350. For a discussion of genetic heterogeneity of GPI biosynthesis defects, see GPIBD1 (610293).

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).

Chronic mucocutaneous candidiasis is characterized by recurrent or persistent infections of the skin, nails, and oral and genital mucosae with Candida albicans, and sometimes by staphylococcal skin infections (summary by Boisson et al., 2013). For a discussion of genetic heterogeneity of familial candidiasis, see CANDF1 (114580).

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).

Immunodeficiency-58 is an autosomal recessive primary immunologic disorder characterized by early-onset skin lesions, including eczematous dermatitis, infectious abscesses, and warts, recurrent respiratory infections or allergies, and chronic persistent infections with candida, Molluscum contagiosum, mycobacteria, EBV, bacteria, and viruses. Some patients may have gastrointestinal involvement, including inflammatory bowel disease, EBV+ smooth muscle tumors, and esophagitis. Immunologic analysis shows defective T-cell function with decreased Treg cells and deficient CD3/CD28 costimulation responses in both CD4+ and CD8+ T cells. B-cell function may also be impaired (summary by Wang et al., 2016 and Alazami et al., 2018).

A rare genetic metabolic liver disease with characteristics of progressive neurodegeneration, cutaneous abnormalities including varying degrees of ichthyosis or seborrheic dermatitis, and systemic iron overload. Patients manifest with infantile-onset seizures, encephalopathy, abnormal eye movements, axial hypotonia with peripheral hypertonia, brisk reflexes, cortical blindness and deafness, myoclonus and hepato/splenomegaly, as well as oral manifestations including microdontia, widely spaced and pointed teeth with delayed eruption and gingival overgrowth.

Agammaglobulinemia-9 (AGM9) is an autosomal recessive primary immunodeficiency characterized by recurrent bacterial infections associated with agammaglobulinemia and absence of circulating B cells. Additional features include failure to thrive and skin involvement. The severity is variable: more severe cases may require hematopoietic stem cell transplantation, whereas others can be treated effectively with Ig replacement therapy (summary by Anzilotti et al., 2019). For a discussion of genetic heterogeneity of autosomal agammaglobulinemia, see AGM1 (601495).