P.72 Motor delays are present in most boys with dystrophinopathies in infancy

Abstract

As clinical trials move into younger cohorts, it is important to understand the degree of motor delay in infants and young children with dystrophinopathy. Identification of appropriate outcome measures will allow quantification of motor skills. This study presents 231 developmental assessments on 112 unique boys with dystrophinopathies using the Gross Motor Subtest of the Bayley Scales of Infant and Toddler Development, Third Edition (Bayley-III). The Bayley-III is a standardized developmental assessment with age-normative values for children between the ages of 16 days and 42 months. Scaled scores range from 1 to 19 with higher scores indicating superior function. While it can be used on older children with developmental delay to quantify skills, the Bayley-III does not provide a scaled score for older children. We completed 140 assessments in individuals within the standard Bayley-III age range with the youngest subject being tested at 2 months. Over 83% of the cohort scored below average as defined by a motor scaled score of 7 or below. The median scaled score was 5 which is 1.33 standard deviations below the mean suggesting a significant delay. One boy scored in the high average range, and he has a mutation that suggests a milder phenotype. In 2019 the Bayley-4 was introduced, key differences from the Bayley-III included an allowance for parent-reported scoring and a polytomous (0-2 point) scoring system. Simultaneously administered same day comparison scores between the Bayley-III and Bayley 4 were highly correlated (Spearman 0.85). This information is critical and will determine feasibility of using previously published Bayley-III data as an external control for future clinical trials.