SDHB and pheochromocytoma-paraganglioma: The majority of hereditary pheochromocytoma and paraganglioma (PPGL) is caused by germline mutations in the SDHB, SDHC, or SDHD genes, which encode three (SDHB, SDHC, SDHD) of five subunits of succinate dehydrogenase (SDH) enzyme (SDHA, SDHDB, SDHC, SDHD, SDHAF2).