SDHB and hereditary pheochromocytoma-paraganglioma: The paraganglioma/pheochromocytoma susceptibility genes include the nuclear genes SDHA, SDHB, SDHC and SDHD, which encode the four subunits of the mitochondrial enzyme succinate dehydrogenase, involved in Krebs cycle oxidative phosphorylation and electron transport in the respiratory chain within mitochondria.