Association between age at loss of ambulation and cardiac function in adults with Duchenne muscular dystrophy

Cardiomyopathy is a common co-morbidity in individuals with Duchenne muscular dystrophy (DMD). This retrospective single centre study investigated the relationship between age at loss of ambulation (LOA) and late stage left ventricular ejection fraction (LVEF) in 84 individuals (> 16 years old) with DMD taking glucocorticoid and ACE inhibitors treatment. Regression analyses showed a positive correlation between later age at LOA and higher LVEF in adulthood (linear regression estimate 1.49, 95 % CI: 0.13-2.84, p = 0.03). Each additional year of ambulation increased the odds of displaying a higher LVEF category (LVEF 40 %, 40 - 50 % or 50 %) by 35 % (p = 0.003). Sensitivity models excluding cardioprotective genotypes (absence of Dp116 isoform) and mild motor phenotypes (out of frame deletions amenable to skip exon 44 and 45) confirmed this association while models including age at respiratory impairment did not improve the model. Individuals who lost ambulation before age 11.92 (ROC AUC 0.73, 95 % CI: 0.60-0.85) reached a LVEF <40 % 5.21 years earlier than those who lost ambulation after that age (adjusted restricted mean survival time 19.08 vs 24.29 years, p < 0.001). These findings may suggest that prolonging ambulation does not impact cardiac function adversely in advance stages of DMD.