HRAS and Noonan syndrome: Mutation in any of them causes several disorders correlated with lymphedema: KRAS heterozygous gain-of-function mutations [52,53] result in Noonan syndrome 3 (OMIM: 609942); NRAS heterozygous gain-of-function mutations [54] result in Noonan syndrome 6 (OMIM: 613224); and HRAS heterozygous gain-of-function mutations [55,56] result in Costello syndrome (OMIM: 218040).