Filamin C (FLNC) is a structural protein that is expressed in striated muscle, providing structural stability to the sarcomere. [1] Pathogenic variants in the FLNC gene have been associated with various disease phenotypes. [2] The genotype-phenotype correlation from pathogenic FLNC variants is modulated by the location of the variant within the FLNC gene, and variants associated with one type of myopathy or cardiomyopathy are not predicted to be able to cause another phenotype. [2] Truncating FLNC variants (FLNCtv) are predicted to cause dilated or arrhythmogenic cardiomyopathy through haploinsufficiency via nonsense-mediated messenger RNA decay which causes weakened structural adhesion.

We report here on a case in which diagnosis of congenital long QT syndrome was facilitated by a smartwatch. A 39-year-old otherwise healthy male patient presented in our outpatient clinic owing to QT prolongation recorded with his smartwatch (ScanWatch; Withings SA, Issy les Moulineaux, France) (Figure 1A and 1B). His medical history was uneventful. He declined palpitations, dyspnea, syncopes, seizures, and family history of sudden cardiac death. He reported to have 2 healthy children aged 7 and 10 years.