SDHB and neuroendocrine neoplasm: Hereditary pheochromocytoma-sympathetic paragangliomas (PPGL) and parasympathetic head & neck paragangliomas (HNPGL) are two distinct neuroendocrine tumour types both primarily caused by variants in succinate dehydrogenase (SDH) subunit genes, all of which are components of a single protein complex of the respiratory chain referred to as Complex II.