PTPN11 and juvenile myelomonocytic leukemia: Fisher et al. found 31 cases published.1Mutation of thePTPN11gene (protein tyrosine phosphatase nonreceptor type 11) and lack of production of the tyrosine phosphatase SHP2 is related with the pathogenesis of metachondromatosis, as well as of other developmental diseases (Noonan syndrome, Noonan syndrome with multiple lentigines) and malignant diseases (juvenile myelomonocytic leukemia).7Mutation of thePTPN11gene is inherited in an autosomal dominant pattern with incomplete penetrance and parents must be advised of it.