The occurrence of SDHB gene mutations in pheochromocytoma

Pheochromocytomas (PCCs) are rare tumors arising from neural crest-derived chromaffin cells. The majority of these tumors are located in the adrenals and gives rise to catecholamine overproduction. In at least 10% of the cases the tumors are located outside the adrenal gland, in extra-adrenal sites like the bladder and the organ of Zuckerkandl. Recent investigations have found mutations in succinate dehydrogenase subunit B (SDHB), the gene coding for subunit B of the respiratory chain complex II. Mutations in the SDHB gene, with additional loss of the wildtype allele, result in loss of function of respiratory complex II and appear to correlate with extra-adrenal location of PCCs. Also, a link has been established between malignant behavior and inactivating mutations of SDHB. In this article we review the published SDHB gene mutations, as well as the location and behavior of the resulting PCCs.