Somatic activating mutations in PTPN11 are the most common cause of sporadic juvenile myelomonocytic leukemia (JMML), a rare but aggressive myelodysplastic and myeloproliferative neoplasm (MPN) occurring in young children (Caye et al., 2015; Tartaglia et al., 2003). The gene discussed is PTPN11; the disease is myeloproliferative disorder.