Missense variants in the PTPN11 gene disrupt normal regulation of the RAS/MAPK pathway and these variants are associated with several human diseases, including LS (Maheshwari et al., 2002; Kontaridis et al., 2006), NS (Tartaglia et al., 2001; Maheshwari et al., 2002) and JMML (Tartaglia et al., 2003). Here, PTPN11 is linked to Leigh syndrome.