An MEN1-like clinical picture can be seen in MEN4 syndrome due to mutation in cyclin dependent kinase inhibitors, primarily p27 (CDKN1B) and rarely in p21 (CDKN1A), p15 (CDKN2B), and p18 (CDKN2C) (108, 109). This evidence concerns the gene CDKN2B and Down syndrome.