Multiple Endocrine Neoplasia Type 4 (MEN4) syndrome has a MEN1-like phenotype, but loss-of-function mutations in the cyclin-dependent kinase inhibitor 1B (CDKN1B) gene are found (encodes p27Kip1, a CDK inhibitor that prevents cell cycle progression from G1 to S phase, thus acting as a tumor suppressor gene) [28]. This evidence concerns the gene CDKN1B and multiple endocrine neoplasia type 4.