Rationale: Variants in TRIM63 , including a nonsense mutation (p.Q247X), have been suggested recently to cause hypertrophic cardiomyopathy. Objective: To verify pathogenicity of TRIM63 p.Q247X detected by whole-exome sequencing in a symptomless professional sports player seeking medical advice because of a prolonged QT interval found during a routine check-up. Methods and Results: Clinical studies were performed in the proband and his mother, who also carried TRIM63 p.Q247X. No evidence of hypertrophic cardiomyopathy was found in either person. Conclusions: The p.Q247X variant in TRIM63 is not likely to be a highly penetrant variant causing hypertrophic cardiomyopathy.