Our findings that pathological activation of MAPK causes lymphangiectasia dovetail with recent studies identifying Noonan’s syndrome patients with chylothorax, lymphedema, and pleural effusion and gain-of-function mutations in components of the MAPK signaling pathway, including ARAF, BRAF, NRAS, HRAS, KRAS, PTPN11, CBL, SOS1, RIT1, RASA1, and SHOC2 (42, 77–88). This evidence concerns the gene HRAS and lymphedema.