To investigate the presence of hypertrophic cardiomyopathy (HCM) at first cardiac evaluation and during follow-up and cardiac events in predictively tested children who are mutation positive.

The study included 119 predictively tested children who were mutation positive, with a mean age of 12.1 years. A family history and clinical variables from all cardiac evaluations after predictive genetic testing were recorded. Outcome measures were a clinical diagnosis of HCM, death, and cardiac events.

No child died during a mean follow-up of 6.9 ± 3.8 years: 95 children were evaluated more than once. Eight (6.7%) children who were mutation positive were diagnosed with HCM at one or more cardiac evaluation(s), some with severe hypertrophy. In one patient who fulfilled the diagnostic criteria for HCM a cardiac event occurred during follow-up. She received an appropriate implantable cardioverter-defibrillator shock 4 years after a prophylactic implantable cardioverter-defibrillator was implanted.

The risk for predictively tested children who are mutation positive to develop HCM during childhood and the risk of cardiac events in children who are phenotype negative are low. In children who are phenotype positive, however, severe hypertrophy and cardiac events can develop. Further research is necessary to study whether the interval between cardiac evaluations in children can be increased after a normal first evaluation and whether risk stratification for sudden cardiac death is necessary in children who are phenotype negative.