Ricotti V, et al. The NorthStar Ambulatory Assessment in Duchenne Muscular Dystrophy: Considerations for the Design of Clinical Trials. J Neurol Neurosurg Psychiatry 2016;87:149–155.
Submitted by David Haustein, MD, News Science Editorial Board
This retrospective study looks into the natural history of motor function in ambulatory boys with Duchenne Muscular Dystrophy (DMD) using the North Star Ambulatory Assessment (NSAA), a 17-item tool that assesses motor function in ambulant boys with DMD. The NSAA has a possible raw score of 0-34 and a linearized version of 0-100 (higher meaning greater function). Using the United Kingdom’s North Star Network data repository, a retrospective analysis of 513 ambulatory UK boys aged 3-16 years old from 2004-2012 was performed. To better understand the natural history using the current standard of care, differences between those boys who had initiated corticosteroids early (before age 5) and later (5-6.5 years old) and by genotype were evaluated. It was found that overall, until the age 7 the boys who were started on steroids typically gained 4 linearized units on the NSAA per year. However, the early starters of corticosteroids experienced greater gains, increasing by 7 linearized units per year, ultimately peaking at 73.8 for the early glucocorticoid users and 68.7 in the late starter group. On average, the boys then experienced an overall rate of decline of 8 linearized units per year thereafter (a change of 10 units being clinically significant), with the median age for loss of ambulation occurring at 13 years old. In a substudy using both Italian and UK data sets, exon 53 and 51 skippable deletions progressed more rapidly, losing 22 and 13 linearized units per year respectively while deletions skippable by exon 44 and 46 followed a more mild course than the average, declining only 9 linearized units over 2 years.
Comment: This study helps quantify the motor gains expected of boys with DMD undergoing both early and late glucocorticoid therapy and can serve as a gauge the standard of care and declines experienced by ambulatory boys with DMD using the NSAA tool; future studies may use this information to gauge the response to therapeutic trials compared to the natural history using the current standard of care. Additionally, the quantification of declines based on genotype will provide further aids in knowing the disease course in patients with specific skippable deletions.
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