Two female siblings (A and B) were referred for clinical screening following the sudden death of their mother aged 45 years from hypertrophic cardiomyopathy (diagnosed post-mortem). The sisters complained of fatigue, exertional dyspnoea (New York Heart Association functional class II), and infrequent palpitations. Their 12 lead ECGs are shown in panels A and B.

In patient A, the echocardiogram demonstrated asymmetric hypertrophy of the interventricular septum …