TNNI3K and Supraventricular tachycardia: To date, genetic variants in TNNI3K have been associated with a mixed clinical picture including DCM, CCD, and (supra)ventricular arrhythmias.1,2,4 In this cohort, most variants in TNNI3K were identified in patients with limited available family history, precluding further cosegregation; which were therefore classified as variants of unknown significance (class 3).22 Based on the increased burden of such variants in our patients, it is likely that a part of these variants contributes to the phenotype of the carriers, especially of those with DCM, CCD, or SVT.