PTPN11 and juvenile myelomonocytic leukemia: It has been established that NS patients are at increased risk of developing childhood myeloproliferative disease (i.e., juvenile myelomonocytic leukemia) and acute leukemia [Tartaglia and Gelb, 2005], and that this specific association is strictly linked to a specific class of activating germline mutations in the PTPN11 gene [Tartaglia et al., 2006].