MYL4 and atrial fibrillation: Several recent studies have suggested genetic testing in some subpopulations of patients with AF (eg, those with early-onset AF).4,5 Genetic studies on familial AF have identified associations with several genes, including the ion-channel gene KCNQ16 and the sarcomere gene MYL4. 7 However, it is difficult to assess the impact of these variants on AF in the general population, and only a few of these findings have been replicated in large-scale, population-based cohort studies.