CS is a rare, developmental disorder and cancer predisposition syndrome that is caused by heterozygous activating mutations in HRAS. CS is one of many conditions, including Noonan syndrome and neurofibromatosis type 1, that result in the overactivation of the Ras pathway and are often referred to as RASopathies (Figure 3) [56]. This evidence concerns the gene HRAS and Cowden syndrome 1.