SDHB and neoplasm: There are differences in incidence (SDHB is commonest), the location of tumor (e.g. SDHD tumors are commoner in the head and neck, while in SDHB, the tumors are equally distributed between the head and neck and adrenal), tendency to metastasise (common in SDHA and SDHB), penetrance (greatest in SDHC, least in SDHB) [25].