Evidence for an Involvement of Cardiomyocyte Hyperplasia Rather than Hypertrophy in Cardiac Enlargement of Noonan Syndrome Patients

Background: Noonan syndrome (NS) is caused by mutations in genes of the RAS/RAF/MAP kinase pathway, such as RAF1 or PTPN11. Apart from variable multisystemic pathologies patients primarily suffer from hypertrophic cardiomyopathy often leading to heart failure. It has been proposed that cardiac enlargement is not solely caused by cardiomyocyte (CM) hypertrophy but that hyperplasia might also contribute. The aim of this study was to evaluate CM morphometry and numbers in postnatal NS myocardium.