Total body and appendicular lean mass by dual-energy X-ray absorptiometry are highly associated with muscle function and bone mineral density in Becker muscular dystrophy

IntroductionBecker muscular dystrophy (Becker) is an X-linked disorder caused by decreased or dysfunctional dystrophin. Data on Dual-energy X-ray absorptiometry (DXA)-derived body composition and the skeletal phenotype are limited. We evaluated associations between DXA-derived height-adjusted body composition and motor function and characterized areal bone mineral density (aBMD) in adolescents and adults with Becker.MethodsIn a cross-sectional, multinational study, ambulatory steroid-naïve participants underwent DXA scans to assess height-adjusted total and appendicular body composition parameters and aBMD at the lumbar spine, total hip, and total body (TB). Motor assessments included the 10-meter walk/run, time-to-rise, North Star Ambulatory Assessment, and Hand-Grip Strength.ResultsTwenty-eight adolescents, median age 15.0 years, interquartile range [IQR] 14.0-16.0, and 38 adults, 28.5 years, IQR 24.3-37.8, were included. Greater TB and lower limb (LL) lean mass indices (LMI) were associated with better motor function, whereas TB and LL fat mass indices (FMI) were negatively associated, with models explaining 20-39% of variance in adolescents and 58-75% in adults. Higher TB-LMI and upper-limb-LMI were associated with greater Hand-Grip strength. In both age groups, the median total hip aBMD and TB z-scores were significantly below the healthy mean, with greatest deficits at the total hip, whereas lumbar spine z-scores did not differ. TB-LMI and LL-LMI were positively associated with total hip aBMD z-scores.ConclusionDXA-derived height-adjusted lean mass is a complementary marker of motor function in Becker. Total hip aBMD appeared to be particularly affected in ambulatory individuals, suggesting it may reflect the underlying myopathy.