Hypertrophic cardiomyopathy in Noonan syndrome.

Noonan syndrome, a well-known multiple congenital anomalies syndrome, is frequently accompanied by cardiovascular diseases including hypertrophic cardiomyopathy (HCM). The incidence of HCM in Noonan syndrome is approximately 20-30% and one-third of cases reveal ventricular outflow obstruction. HCM in Noonan syndrome is occasionally associated with a congenital heart defect, whereas classic HCM seldom accompanies cardiac malformations. Asymmetric septal hypertrophy and symmetric septal hypertrophy (concentric hypertrophy) can be observed both in HCM with Noonan syndrome and in classic HCM, but apical hypertrophy has not been reported in Noonan syndrome yet, although it appears in classic HCM. Congestive heart failure is the major cause of death in patients with HCM in Noonan syndrome, but cases of sudden death have also been reported. The histopathologic findings of ventricular myocardial tissue in HCM with Noonan syndrome are similar to those in classic HCM.