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.

Autoimmune polyglandular syndrome type I (APS1) is characterized by the presence of 2 of 3 major clinical symptoms: Addison disease, and/or hypoparathyroidism, and/or chronic mucocutaneous candidiasis (Neufeld et al., 1981). However, variable APS1 phenotypes have been observed, even among sibs. In addition, some patients may exhibit apparent isolated hypoparathyroidism, an early manifestation of APS1 with peak incidence at around age 5 years; over long-term follow-up, the development of additional features of APS1 may be observed (Cranston et al., 2022).

Autosomal dominant hypocalcemia-1 (HYPOC1) is associated with low or normal serum parathyroid hormone concentrations (PTH). Approximately 50% of patients have mild or asymptomatic hypocalcemia; about 50% have paresthesias, carpopedal spasm, and seizures; about 10% have hypercalciuria with nephrocalcinosis or kidney stones; and more than 35% have ectopic and basal ganglia calcifications (summary by Nesbit et al., 2013). Thakker (2001) noted that patients with gain-of-function mutations in the CASR gene, resulting in generally asymptomatic hypocalcemia with hypercalciuria, have low-normal serum PTH concentrations and have often been diagnosed with hypoparathyroidism because of the insensitivity of earlier PTH assays. Because treatment with vitamin D to correct the hypocalcemia in these patients causes hypercalciuria, nephrocalcinosis, and renal impairment, these patients need to be distinguished from those with other forms of hypoparathyroidism (see 146200). Thakker (2001) suggested the designation 'autosomal dominant hypocalcemic hypercalciuria' for this CASR-related disorder. Genetic Heterogeneity of Autosomal Dominant Hypocalcemia Autosomal dominant hypocalcemia-2 (HYPOC2; 615361) is caused by mutation in the GNA11 gene (139313) on chromosome 19p13.

Hereditary hypophosphatemic rickets with hypercalciuria (HHRH) is a rare autosomal recessive disorder characterized by the presence of hypophosphatemia secondary to renal phosphate wasting, radiographic and/or histologic evidence of rickets, limb deformities, muscle weakness, and bone pain. HHRH is distinct from other forms of hypophosphatemic rickets in that affected individuals present with hypercalciuria due to increased serum 1,25-dihydroxyvitamin D levels and increased intestinal calcium absorption (summary by Bergwitz et al., 2006).

Hypoparathyroidism-retardation-dysmorphism syndrome (HRDS) is an autosomal recessive multisystem disorder characterized by intrauterine and postnatal growth retardation, infantile-onset hypoparathyroidism that can result in severe hypocalcemic seizures, dysmorphic facial features, and developmental delay (summary by Padidela et al., 2009 and Ratbi et al., 2015).

Infantile hypercalcemia is characterized by severe hypercalcemia, failure to thrive, vomiting, dehydration, and nephrocalcinosis. An epidemic of idiopathic infantile hypercalcemia occurred in the United Kingdom in the 1950s after the implementation of an increased prophylactic dose of vitamin D supplementation; however, the fact that most infants receiving the prophylaxis remained unaffected suggested that an intrinsic hypersensitivity to vitamin D might be implicated in the pathogenesis (summary by Schlingmann et al., 2011). Genetic Heterogeneity Infantile hypercalcemia-2 (HCINF2; 616963) is caused by mutation in the SLC34A1 gene (182309) on chromosome 5q35.

Garfield and Karaplis (2001) reviewed the various causes and clinical forms of hypoparathyroidism. They noted that hypoparathyroidism is a clinical disorder characterized by hypocalcemia and hyperphosphatemia. It manifests when parathyroid hormone (PTH; 168450) secreted from the parathyroid glands is insufficient to maintain normal extracellular fluid calcium concentrations or, less commonly, when PTH is unable to function optimally in target tissues, despite adequate circulating levels. Genetic Heterogeneity of Familial Isolated Hypoparathyroidism FIH2 (618883) is caused by mutation in the GCM2 gene (603716). An X-linked form of familial hypoparathyroidism, HYPX (307700), is caused by interstitial deletion/insertion on chromosome Xq27.1, which may have a position effect on expression of SOX3 (313430). Congenital absence of the parathyroid and thymus glands (III and IV pharyngeal pouch syndrome, or DiGeorge syndrome, 188400) is usually a sporadic condition (Taitz et al., 1966).

Patients with familial isolated hypoparathyroidism-2 (FIH2) usually present with seizures, caused by hypocalcemia, in early life. Serum parathyroid hormone (PTH; 168450) levels are low to undetectable. Hyperphosphatemia is present, and levels of 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D may be within the normal range. Development can be normal if hypocalcemia is treated with calcium and vitamin D supplementation (Ding et al., 2001). Some patients have been found to lack parathyroid glands (Thomee et al., 2005). For a discussion of genetic heterogeneity of familial isolated hypoparathyroidism, see FIH1 (146200).