Hereditary MTC forms (~25% of cases) are caused by inherited autosomal dominant germline pathogenic variants in the RET proto-oncogene and are subclassified into Multiple Endocrine Neoplasia (MEN) type 2A and type 2B and Familial MTC (FMTC), respectively. The gene discussed is RET; the disease is medullary thyroid gland carcinoma.