PTPN11 and Noonan syndrome: However, non-penetrance is not restricted to the mutations we described, but is, rather, a common feature in most, if not all, of the described genes that may cause CHD in humans such as PTPN11 in Noonan Syndrome [47], KCNQ1 in Long QT Syndrome [48] and troponin T in Familial Hypertrophic Cardiomyopathy [49].