RET and multiple endocrine neoplasia type 2A: In 1993, it was found that germline gain-of-function mutations in the RET proto-oncogene, which encodes a receptor tyrosine-kinase expressed in the derivatives and tumors of neural crest origin, are the genetic cause of 98% of MEN2A and ~95% of FMTC families [3,4], while the remaining 2–5% of clinically MEN2A and FMTC families do not carry RET mutations [5,6].