The pressure rises: update on the genetics of phaeochromocytoma

Phaeochromocytomas are neoplasias of neural crest origin arising from the adrenal medulla. Extra-adrenal phaeochromocytomas occur and may be referred to as paragangliomas, although this term is also used to describe vascular head and neck tumours, which most commonly develop at the carotid bifurcation. Historically, genetic factors have been implicated in up to 10% of phaeochromocytoma cases, but recent data suggest that germline mutations may be detected in approximately 25% of unselected cases. The most frequent causes of phaeochromocytoma susceptibility are von Hippel-Lindau disease (VHL), multiple endocrine neoplasia type 2 (MEN 2), the newly delineated phaeochromocytoma-paraganglioma syndrome and, less commonly, neurofibromatosis type 1. Germline mutations in three of the succinate dehydrogenase (SDH, mitochondrial complex II) subunits (SDHD, SDHB and SDHC) cause susceptibility to head and neck paragangliomas, and may be found in approximately 20% of unselected patients. In addition, germline SDHD and SDHB mutations may cause phaeochromocytoma susceptibility with or without associated head and neck paragangliomas. Recent studies suggest that germline SDHD and SDHB mutations are an important cause of familial and isolated phaeochromocytoma. The mechanism by which SDH subunit mutations predispose to phaeochromocytomas has not been defined in detail, but dysregulation of hypoxia-responsive genes and impairment of mitochondria-mediated apoptosis have both been suggested.