Noonan and Noonan-like syndromes are multisystem genetic disorders, mainly with autosomal dominant trasmission, caused by mutations in several genes: PTPN11 (OMIM 176,876), KRAS (OMIM 190,070), SOS1 (OMIM 182,530), RAF1 (OMIM 164,760), NRAS (OMIM 164,790), BRAF (OMIM 164,757), RIT1 (OMIM 609,591), SOS2 (OMIM 601,247), LZTR1 (OMIM 600,574), MRAS (OMIM 608,435), RRAS2 (OMIM 165,090), MAPK1 (OMIM 176,948), RRAS2 (OMIM 600,098), A2ML1 (OMIM 616,027), CBL (OMIM 165,360), SHOC2 (OMIM 602,775), PPP1CB (OMIM 600,590). The gene discussed is SOS1; the disease is Noonan syndrome.