Inherited mutations in the RET gene are instead associated exclusively with familial forms of medullary thyroid carcinoma (MTC), which, unlike other malignant thyroid neoplasms, originates from the parafollicular cells of the thyroid gland and with multiple endocrine neoplasia syndrome (MEN2A and MEN2B)-inherited diseases that lead to further abnormal activation of one or more endocrine glands [43,44,45]. The gene discussed is RET; the disease is multiple endocrine neoplasia.