Approximately 5% of all cases of primary hyperparathyroidism (pHPTH) are hereditary. Most patients with a hereditary form of the clisease have a family history suggestive of the disease, however, isolated cases may also have a genetic predisposition due to a de novo mutation or a somatic/germline mosaic state. They are generally characterized by pHPTH that affect men as often as women at an earlier age of onset. There may be an association with other (multicentric) tumors (Figure 9.1). Hereditary pHPTH syndromes are outlined below, after a brief introduction to cancer genetics. Guide to diagnosis of hereditary primary hyperparathyroidism (pHPTH) syndromes. Ascertain whether the same individual or first-degree relatives have any other endocrine tumors or other associated manifestations and perform the appropriate genetic testing. This is done on DNA isolated from peripheral blood in an EDTA-tube. * If C-cell hyperplasia, exclude secondary hyperplasia due to HPTH, chronic lymphocytic thyroiditis, hypergastrinemia, near-follicular–derived tumors, and aging. EPT, enteropancreatic endocrine tumor; HPTH, hyperparathyroidism; MTC, medullary thyroid carcinoma; CCH, C-cell hyperplasia; MEN1, multiple endocrine neoplasia type 1; HPT-JT, hyperparathyroidism and jaw tumor syndrome; MEN2, multiple endocrine neoplasia type 2; FIHP, familial isolated hyperparathyroidism. https://s3-euw1-ap-pe-df-pch-content-public-u.s3.eu-west-1.amazonaws.com/9780429098260/f7dd27ea-9ce5-4b5c-9b1f-612e605e8546/content/fig9_1.tif"/>