Accelerated Cardiomyocyte Proliferation in the Heart of a Neonate With LEOPARD Syndrome-Associated Fatal Cardiomyopathy.

LEOPARD syndrome (LS) is a form of RASopathy caused by mutations in the PTPN11 gene an upstream regulator of RAS/MAPK signaling. Although hypertrophic cardiomyopathy (HCM) is a shared cardiac phenotype among RASopathies, HCM complicating patients with LS is characteristic for its unique early-onset and progressive features.We herein report a neonate with LS who presented with an extremely severe form of HCM. Autopsy revealed remarkable evidence of active cardiomyocyte proliferation contributing to the overt cardiomegaly. The case suggests an intriguing association between the observed dramatic increase in cardiomyocyte mitotic activity and the fatal clinical course of LS-associated HCM.The patient was the second daughter born to nonconsanguineous parents with no significant family history. Marked biventricular hypertrophy was noted on fetal echocardiography at the 28th week of gestation. After an uneventful delivery, the patient was immediately admitted to the neonatal intensive care unit. Physical examination at birth revealed multiple dysmorphic features, including a wide forehead, low set ears, hypertelorism, and wide set nipples. No skin lesions, such as cafe-au-lait spots or lentigines, were noticed, whereas mild hearing loss was detected by newborn screening. The findings were suggestive of LS. Imaging studies were remarkable for cardiomegaly (Figure …