Multiple endocrine neoplasia type 2 (MEN2) includes the following phenotypes: MEN2A, familial medullary thyroid carcinoma (FMTC, which may be a variant of MEN2A), and MEN2B. All three phenotypes involve high risk for development of medullary carcinoma of the thyroid (MTC); MEN2A and MEN2B involve an increased risk for pheochromocytoma; MEN2A involves an increased risk for parathyroid adenoma or hyperplasia. Additional features of MEN2B include mucosal neuromas of the lips and tongue, distinctive facies with enlarged lips, ganglioneuromatosis of the gastrointestinal tract, and a marfanoid habitus. MTC typically occurs in early childhood in MEN2B, early adulthood in MEN2A, and middle age in FMTC.

Hyperphosphatemic familial tumoral calcinosis (HFTC) is a rare autosomal recessive metabolic disorder characterized by the progressive deposition of basic calcium phosphate crystals in periarticular spaces, soft tissues, and sometimes bone (Chefetz et al., 2005). The biochemical hallmark of tumoral calcinosis is hyperphosphatemia caused by increased renal absorption of phosphate due to loss-of-function mutations in the FGF23 (605380) or GALNT3 (601756) gene. The term 'hyperostosis-hyperphosphatemia syndrome' (HHS) is sometimes used when the disorder is characterized by involvement of the long bones associated with the radiographic findings of periosteal reaction and cortical hyperostosis. Although some have distinguished HHS from FTC by the presence of bone involvement and the absence of skin involvement (Frishberg et al., 2005), Ichikawa et al. (2010) concluded that the 2 entities represent a continuous spectrum of the same disease, best described as familial hyperphosphatemic tumoral calcinosis. HFTC is considered to be the clinical converse of autosomal dominant hypophosphatemic rickets (ADHR; 193100), an allelic disorder caused by gain-of-function mutations in the FGF23 gene and associated with hypophosphatemia and decreased renal phosphate absorption (Chefetz et al., 2005; Ichikawa et al., 2005). For a general phenotypic description and a discussion of genetic heterogeneity of HFTC, see 211900.