TNNI3 and KCNQ1 co-inherited variants in a family with hypertrophic cardiomyopathy and long QT phenotypes: A case report.

QTc prolongation is reported in patients with hypertrophic cardiomyopathy (HCM). However, the causes of the QTc interval increase remain unclear. The main contribution to QTc prolongation in HCM is attributed to the myocardial hypertrophy and related structural damage. In a 24-year-old male proband, affected by HCM and long QTc, we identified by Next Generation Sequencing a pathogenic variant in gene TNNI3 co-inherited with a damaging variant in KCNQ1 gene. This evidence suggests the possibility that QTc interval prolongation and its dispersion in HCM could be associated not only to the severity of left ventricular hypertrophy but also to the co-inheritance of pathogenic variants related to both long QT Syndrome (LQTS) and HCM. Although the simultaneous presence of pathogenic variants in genes related to different heart diseases is extremely rare, counseling and genetic testing appear crucial for the clinical diagnosis. Screening of LQTS genes should be considered in HCM patients to clarify the origin of long QTc, to provide more information about the clinical presentation and to evaluate the incidence of the co-existence of LQTS/HCM gene variants that could occur more frequently than so far reported.