Co-occurrence of hypertrophic cardiomyopathy and juvenile myelomonocytic leukemia in a neonate with Noonan syndrome, leading to premature death

Key Clinical Message We report a case of a neonate with Noonan syndrome presenting with concurrent hypertrophic cardiomyopathy and juvenile myelomonocytic leukemia, which resulted in premature death. Cases with Noonan syndrome diagnosed during the neonatal period might not necessarily show mild clinical course, and premature death is a possible outcome to be considered.