A recent study published in Circulation suggests that clinical testing of kids who are first degree family members of HCM patients (i.e. siblings and children of those who have already been diagnosed with HCM) could be improved by starting testing at a younger age. And, genetic testing should further improve diagnosis and treatment for this group.
Almost 5% of children included in this study were diagnosed with HCM at the time of their initial screening. The majority of these children (72%) had not yet reached the age of adolescence. Childhood diagnoses were not that unusual in this sample: a childhood diagnosis was made in 8% of families that were screened.
Hence, this article suggest that regular screenings of youth in HCM families should start before age 10. Note that current ACCF/AHA Guidelines followed in the U.S. (published in 2011 and set to be updated next year) make screening before age 12 optional. The 2014 ESC guidelines followed in Europe recommend screening of children in HCM families from age 10 onward, unless there is a particularly bad family history or other factors which might call for heightened scrutiny.