Predictors and prevalence of paraganglioma syndrome associated with mutations of the SDHC gene

Context Paraganglioma syndrome includes inherited head and neck paragangliomas (HNPs) and adrenal or extra-adrenal pheochromocytomas and are classified according to the susceptibility genes SDHB, SDHC, and SDHD. In contrast with those with germline mutations of the SDHB and SDHD genes, clinical and genetic data on patients with mutations of SDHC are scarce. Objective To determine the prevalence and clinical characteristics of SDHC mutation carriers compared with patients with SDHB and SDHD mutations and with sporadic cases. Design, Setting, and Patients Genetic screening for SDHC mutations in an international HNP registry of 121 unrelated index cases and in 371 sporadic cases from a pheochromocytoma registry, conducted January 1, 2001, until December 31, 2004. Identified index cases and affected relatives were clinically evaluated. Main Outcome Measures Prevalence of and clinical findings for SDHC mutation-associated HNPs vs those with SDHB and SDHD mutations. Results The prevalence of SDHC carriers was 4% in HNP but 0% in pheochromocytoma index cases. None of the SDHC mutation carriers had signs of pheochromocytoma. We compared HNPs in 22 SDHC mutation carriers with the HNPs of SDHB (n=15) and SDHD (n=42) mutation carriers and with 90 patients with sporadic HNPs. Location, number of tumors, malignancy, and age were different: more carotid body tumors were found in SDHC (13/22 [59%]) than in sporadic HNPs (29/90 [32%], P=.03), as well as fewer instances of multiple tumors in SDHC (2/22) than in SDHD (24/42; P<.001), 0 malignant tumors in SDHC vs 6/15 in SDHB (P=.002), and younger age at diagnosis in SDHC than in sporadic HNPs (45 vs 52 years; P=.03). Conclusions Patients with HNP, but not those with pheochromocytoma, harbor SDHC mutations in addition to those in SDHB and SDHD. In total, more than one quarter of HNP patients carry a mutation in 1 of these 3 genes. Head and neck paragangliomas associated with SDHC mutations are virtually exclusively benign and seldom multifocal. Analysis for germline mutations of SDHC is recommended in apparently sporadic HNP to identify risk of inheritance.