Graphic representation of mutation prevalence among individuals bearing PTPN11 mutations with Noonan syndrome (NS), childhood leukemia, and LEOPARD syndrome (LS). (A) PTPN11 mutations observed in NS are distributed widely throughout the PTPN11 gene, with the most common affected residue being glutamine (N) 308 (based on 175 patients with NS identified with PTPN11 mutations). (B) PTPN11 mutations observed in childhood leukemias are clustered within exons 3 and 13 (based on 163 patients with pediatric leukemia identified with PTPN11 mutations). (C) The vast majority of PTPN11 mutations observed in LS involve residues tyrosine (Y) 279 and threonine (T) 468 (based on 63 patients with LS identified with PTPN11 mutations).