MAP2K1 and Noonan syndrome: Over the years, several other genes involved in Noonan syndrome (<i>KRAS</i>, <i>SOS1</i>, <i>RAF1</i>, <i>MAP2K1</i>, <i>BRAF</i>, <i>NRAS</i>, <i>RIT1</i>, and <i>LZTR1</i>) have been identified, acting at different levels of the RAS-mitogen-activated protein kinase pathway.