TNNI3 and hypertrophy: To illustrate the importance of identifying subclinical disease in carriers of the TNNI3 p.Arg21Cys mutation who have no hypertrophy on echocardiogram, we obtained Doppler tissue imaging (DTI) and cardiac magnetic resonance imaging (MRI) on 2 carriers of the mutation, a 13-year-old adolescent (patient III-18 from DH232-A) with no hypertrophy on echocardiogram and, therefore, no clinical diagnosis of HCM before the study, and a 48-year-old man (patient II-1 from DH232-A) with symptomatic HCM (Figures 3 and 4).