Neonatal severe hyperparathyroidism usually manifests in the first 6 months of life with severe hypercalcemia, bone demineralization, and failure to thrive. Early diagnosis is critical because untreated NSHPT can be a devastating neurodevelopmental disorder, which in some cases is lethal without parathyroidectomy. Some infants have milder hyperparathyroidism and a substantially milder clinical presentation and natural history (summary by Egbuna and Brown, 2008).

Any familial hypocalciuric hypercalcemia in which the cause of the disease is a mutation in the AP2S1 gene.

Familial hypocalciuric hypercalcemia type II (HHC2) is an autosomal dominant disorder characterized by lifelong elevations of serum calcium concentrations with low urinary calcium excretion and normal circulating parathyroid hormone concentrations in most patients. Patients are generally asymptomatic (summary by Nesbit et al., 2013). For a general phenotypic description and a discussion of genetic heterogeneity of hypocalciuric hypercalcemia, see HHC1 (145980).

The spectrum of CDC73-related disorders includes the following phenotypes: Hyperparathyroidism-jaw tumor (HPT-JT) syndrome. Primary hyperparathyroidism occurs in a vast majority of affected individuals, with onset typically in late adolescence or early adulthood. HPT-JT syndrome-associated primary hyperparathyroidism is usually caused by a single parathyroid adenoma. In at least 10%-15% of individuals, primary hyperparathyroidism is caused by parathyroid carcinoma. Ossifying fibromas of the mandible or maxilla, also known as cementifying fibromas and cemento-ossifying fibromas, occur in 30%-40% of individuals with HPT-JT syndrome. Although benign, these tumors can be locally aggressive and may continue to enlarge if not treated. Up to 20% of individuals with HPT-JT syndrome have kidney lesions, most commonly cysts; renal hamartomas and (more rarely) Wilms tumor have also been reported. Benign uterine tumors appear to be common in women with HPT-JT syndrome; uterine malignancies have also been reported. Parathyroid carcinoma. Most parathyroid carcinomas are functional, resulting in primary hyperparathyroidism and a high serum calcium level; however, nonfunctioning parathyroid carcinomas are also rarely described in individuals with a CDC73-related disorder. A germline CDC73 pathogenic variant has been identified in 20%-29% of individuals with parathyroid carcinoma without a known family history of CDC73-related conditions. Familial isolated hyperparathyroidism (FIHP). Characterized by primary hyperparathyroidism without other associated syndromic features. Individuals with CDC73-related FIHP tend to have a more severe clinical presentation and younger age of onset than individuals with FIHP in whom a CDC73 pathogenic variant has not been identified.

Multiple endocrine neoplasia type 4 (MEN4) is characterized by the development of endocrine tumors, especially those involving the parathyroid and/or pituitary gland. Parathyroid adenomas and parathyroid hyperplasia manifest as hypercalcemia (primary hyperparathyroidism) as a result of the overproduction of parathyroid hormone. Anterior pituitary adenomas can secrete adrenocorticotrophic hormone (ACTH), growth hormone (GH), prolactin, or are nonfunctional (nonsecreting) adenomas. Well-differentiated endocrine tumors of the gastroenteropancreatic tract, carcinoid tumors, and adrenocortical tumors can also occur.

Any familial isolated hyperparathyroidism in which the cause of the disease is a mutation in the GCM2 gene.