PTPN11 and Leigh syndrome: Noonan syndrome and LS are heterogenous autosomal dominant diseases caused by mutations in several genes, including the CPG, PTPN11. PTPN11 encodes the ubiquitously expressed Src homology region 2 domain containing phosphatase-2 (SHP2), a protein tyrosine phosphatase involved in relaying growth signals and activating RAS and the MAPK/ERK pathway (Neel et al., 2003; Figure 4).