In a report, Maron et al. tell us that the number of adult patients reported with delayed-onset left ventricular hypertrophy (LVH) has been relatively small and that it would be expected that most relatives of patients with hypertrophic cardiomyopathy (HC) with normal imaging and electrocardiographic findings at 18 years of age will be genetically unaffected. This opinion is not supported by data from a recently published cohort of Dutch HC mutation carriers.

According to the American College of Cardiology Foundation/American Heart Association (ACCF/AHA) Guideline and the American College of Cardiology/European Society of Cardiology (ACC/ESC) Clinical Expert Consensus Document on Hypertrophic Cardiomyopathy, all HC family members should undergo a cardiac evaluation during adolescence. And, because of the possibility of delayed adult-onset LVH, it is recommended that adult relatives with normal echocardiograms at or beyond age 18 years have subsequent clinical studies performed once every 5 years. In the Netherlands, this is the current policy. Because of this current screening policy and the possibility of DNA-diagnostics and cascade screening, we have access to cardiac follow-up data of many HC mutation carriers, including asymptomatic family members.

The latest publication on our national database reports on 446 predictively tested HC mutation carriers. Three hundred thirty-nine carriers (76.0%) with a mean age of 37.4 ± 17.1 years had no HC phenotype at the first cardiac evaluation. Twenty-nine (mean age at first cardiac evaluation 45.0 ± 16.0 years) of these 339 carriers (8.6%) developed LVH during an average total follow-up of 2.2 ± 1.6 years. In all these carriers, the onset of LVH occurred in all but one after adolescence (mean age of onset 45.4 ± 16.0 years, range 10 to 71).

In conclusion, we found that even during a limited time of follow-up, a significant number of HC mutation carriers develop an HC phenotype after adolescence. Besides, most of predictively tested mutation carriers still have no phenotype in adulthood. Therefore, it is important to continue screening after adolescence when there is no HC phenotype at the initial evaluation. We are pleased to see that Maron et al. share this view; however, negative echo findings after adolescence are more common in HC mutation carriers than previously believed.