MEN2 has two subtypes: MEN2A (OMIM 171400) accounts for ∼90–95% of cases including a less penetrant sub-form (familial medullary thyroid carcinoma, FMTC [2], [3]), while MEN2B (OMIM 162300) makes up the remaining ∼5–10%. Here, RET is linked to familial medullary thyroid carcinoma.