AKT1 and Noonan syndrome: Despite these caveats, MC could be locus heterogeneous, similar to Noonan syndrome, which can be caused by mutations in PTPN11 or in other components of the Ras/MAPK pathway [28]; however, our targeted capture and sequencing of 74 genes that included most of the Ras/MAPK and PI3K/Akt signaling pathways did not find an obvious mutation in another gene in any of the 6 PTPN11 mutation-negative MC patients.