Sex Differences in Cardiac Involvement in Adults With Myotonic Dystrophy Type 1: A Multicenter Study

Myotonic dystrophy type 1 (DM1) is associated with progressive cardiac conduction abnormalities (CCAs) and arrhythmias. Although genetic anticipation and CTG repeat length influence disease severity, sex-related differences in cardiac involvement remain underexplored.

We aimed to investigate sex differences in cardiac outcomes in a large cohort of adult DM1 patients and assess whether these differences persist after adjustment for generational effects.

Clinical data from 549 DM1 patients followed at 16 inherited cardiac disease clinics in Spain were analyzed. The primary endpoint was a composite of lifetime CCA development, device implantation, major ventricular arrhythmias, and cardiac syncope. Secondary endpoints included overall survival, atrial fibrillation (AF), and device implantation. Birth cohort (representing generation) was used as a surrogate for underlying genetic burden, as later generations tend to accumulate larger CTG expansions.

When compared to females, males had a higher cumulative incidence of the primary endpoint (subdistribution HR [sHR]: 1.50; 95% CI: 1.12-2.00; P = 0.006), device implantation (sHR: 1.49; 95% CI: 1.04-2.14; P = 0.029) and AF (sHR: 2.19; 95% CI: 1.36-3.53; P = 0.001). Males more commonly presented with first-degree atrioventricular block compared to females (46.7% vs 37.9%; P = 0.037), but there was no significant difference in second- or third-degree atrioventricular block or QRS ≥120 ms. Sex differences in primary endpoint, device implantation, and AF persisted after generational adjustment (all P < 0.05). Overall survival was similar between sexes (P = 0.472).

In this large DM1 cohort, male sex was associated with a higher cumulative incidence of earlier CCA, device implantantion, and AF, beyond generational/genetic effects. These findings support sex-informed risk stratification.