Specifically, in a retrospective cohort study of 69 patients with DMD and BMD (of which 47 had genetic analysis of their deoxyribonucleic acid [DNA]), Jefferies et al. [24] investigated the association between DMD mutations and age at onset of cardiomyopathy (defined as EF < 55% or left ventricular dilation). This evidence concerns the gene DMD and cardiomyopathy.