Background: Previous studies in adults with Becker Muscular Dystrophy (BMD) demonstrated variable clinical severity in genotype subgroups: “mild” group for exon deletions end at exon 51 (x-51) and “severe” groups for deletions begin at exon 45 (45-x) and mutations in domain 1(promoter through exon 9). Better delineation of motor function in pediatric BMD can inform clinical consultation and trial design.
Objectives: We aim to characterize the motor function and genotype-phenotype correlations in pediatric BMD.
Methods: This is a retrospective study of electronic health records of 86 individuals with pediatric BMD with encounters from 7/1/2008 to 4/30/2022. Data collected include demographics, genetic testing and motor function measures: North Star Ambulatory Assessment (NSAA), 10-meter walk/run, 4-stair climb and Gowers’ maneuver. Data were analyzed via multiple linear regression and repeated measures model.
Results: The earliest significant difference in “severe” BMD versus the cohort was shown in the 4-stair climb ascent and 10-meter walk/run at age 8 years. The group with 45-x deletions and mutations involving domain 1 performed worse than the rest of cohort in all measures, with the earliest significant difference seen in 4-stair climb at age 9. Those with deletions x-51 demonstrated better performance in the 10-meter walk/run and NSAA when compared against the deletion 45-x and domain 1 group.
Conclusions: A subgroup of “severe” BMD differed from the rest at as early as age 8 years. Consistent with previous adult data, those with 45-x deletion and domain 1 mutations had worse motor function. X-51 deletion had a milder motor phenotype. The4-stair climb ascending is the most consistently identified measure showed difference at the earliest age.