RET and multiple endocrine neoplasia type 2A: Genetically, MEN2A syndromes are caused by pathogenic germline RET variants, the most common of which contain activating mutations in one of six cysteine codons in the extracellular domain (codons 609, 611, 618, 620, 630, and 634 account for more than 98% of MEN2A cases) (1, 2, 3).