Penetrance of Hypertrophic Cardiomyopathy in Children and Adolescents A 12-Year Follow-up Study of Clinical Screening and Predictive Genetic Testing

Background-The penetrance of hypertrophic cardiomyopathy (HCM) during childhood and adolescence has been only sparsely described. We studied the penetrance of HCM and the short- and long-term outcomes of clinical screening and predictive genetic testing of child relatives of patients with HCM. Methods and Results-Ninety probands and 361 relatives were included in a family screening program for HCM (19942001). Eleven sarcomere genes, CRYAB, alpha-GAL, and titin were screened. Sixty-six relatives and 4 probands were <18 years of age at inclusion. Twelve child relatives were mutation carriers (age, 12 +/- 5 years), and 26 had unknown genetic status, ie, relatives from families without identified mutations (n = 21) or not tested (n = 5) (age, 11 +/- 5 years). Twenty-eight noncarriers (42%; age, 10 +/- 4 years) served as control subjects. Two of 38 child relatives (5%) at risk of developing HCM fulfilled diagnostic criteria for HCM at inclusion. After 12 +/- 1 years of follow-up, 2 of the 36 (6%; 95% confidence interval, 2-18) at-risk child relatives who were phenotype negative at inclusion had developed the HCM phenotype at 26 and 28 years of age. During follow-up, none of the child relatives experienced serious cardiac events. Participation in the screening program had no long-term negative psychological impact. Conclusions-The penetrance of HCM in phenotype-negative child relatives at risk of developing HCM was 6% after 12 years of follow-up. The finding of phenotype conversion in the mid-20s warrants continued screening into adulthood. Forty-two percent of the child relatives were noncarriers, and repeat clinical follow-up could be safely limited to the remaining children. (Circulation. 2013;127:48-54.)