The co-occurrence of neurodevelopmental problems in dyslexia: The rule or the exception?

Abstract: The main purpose of this study was to explore the overlap between dyslexia and a range of neurodevelopmental problems (NDPs), specifically symptoms of attention-deficit/ hyperactivity disorder (ADHD), autism spectrum disorder (ASD), atypical sensory perception (ASP) and developmental coordination disorder (DCD). Capitalizing on a population-based sample of twins, complementing aims included calculating the heritability of dyslexia and re-evaluating the Short Dyslexia Scale (SDS). A telephone interview regarding dyslexia and other NDPs was conducted with parents of 1688 nine-year-old twins. The prevalence of dyslexia was ca 8% and the heritability of dyslexia was estimated at 52%. There was a 10-fold increase in diagnostic proxy NDPs in the dyslexia group compared to typical readers. Quantitatively measured symptoms of inattention, oral language problems, and ASP significantly predicted dyslexia status in a multivariate analysis. By contrast, ASD-related inflexibility/circumscribed interests were inversely associated with dyslexia in a multifactorial model. Taken together, dyslexia is a heritable condition that often overlaps with other NDPs. Moreover, there may be a need to move beyond isolated diagnostic categories into behavioral profiles when trying to understand the pattern of strengths and needs in individuals and groups with dyslexia.