The co‐occurrence of neurodevelopmental problems in dyslexia

Abstract

The primary aim of this study was to explore the overlaps between dyslexia and a range of neurodevelopmental disorders and problems (NDPs), specifically symptoms of attention‐deficit/hyperactivity disorder, autism spectrum disorder, atypical sensory perception and developmental coordination disorder. Capitalizing on a population‐based sample of twins, secondary aims included estimating the heritability of dyslexia and reporting on the measurement characteristics of the scale used to assess dyslexia. A telephone interview regarding symptoms of dyslexia and other NDPs was conducted with parents of 1,688 nine‐year‐old twins. The prevalence and the heritability of dyslexia were estimated at 8 and 52%, respectively. The boy: girl ratio was 1.5:1. Results revealed that there was more than an eight‐fold increase in (diagnostic proxy) NDPs prevalence in the dyslexia group as compared to typical readers. Quantitatively measured symptoms of inattention, oral language problems and atypical sensory perception significantly predicted dyslexia status in a multivariate analysis. By contrast, ASD‐related inflexibility was inversely associated with dyslexia in the multivariate model. In sum, dyslexia often overlaps with other NDPs. The current study provides new knowledge supporting the position to move beyond isolated diagnostic categories into behavioural profiles of co‐occurring problems when trying to understand the pattern of strengths and needs in individuals with dyslexia.

Prevalence of Reading Difficulties in 9- to 10-Year Old Children in Sweden Born With Cleft Palate

“…To estimate the internal reliability of test scores on the SDS, a Cronbach α test was performed, which indicated excellent internal consistency (α = .91). This corresponds to the internal consistency rate of the 2 other studies that have used the same questionnaire (Brimo et al, 2021; Parra & Wass, 2016). For an item-by-item frequency of answers on the SDS, see Figure 1.…”

“…The current study replicates earlier studies concerning prevalence of reading difficulties and cleft type (Richman et al, 1988; Broder et al, 1998; Conrad, 2019). Reading difficulties are more prevalent in the total study group (22%) than in the general population (where ca 7%-10% are affected) and results from the study can be compared to 2 earlier studies using the same SDS in 2 community samples where the prevalence rate of reading difficulties in those study groups were 9.5% (n = 136; Parra & Wass, 2016) and 7.6% (n = 1688; Brimo et al, 2021), respectively.…”

“…The questionnaire is based on slightly revised items from 2 preexisting questionnaires: Five to fifteen (Kadesjö et al, 2004) and Colorado Learning Difficulties Questionnaire (Willcutt et al, 2011) and compiled by Åsberg Johnels and Lundström (unpub). The questionnaire has a high internal consistency (Cronbach α = .87), moderate to strong correlations in relation to established Swedish clinical tests of reading and spelling (including phonological and orthographic skills), and is validated in a community sample of 9-year olds (Parra & Wass, 2016) and in the Child and Adolescent Twin Study in Sweden with current data from approximately 1600 nine-year-old children with a population-based prevalence of reading difficulties at approximately 8% (Brimo et al, 2021). Analysis of area under the curve showed that the questionnaire had a high diagnostic accuracy of 0.80 ( P < .001), that is, it adequately discriminates between cases with and without dyslexic reading difficulties defined by test scores of <10th percentile (Parra & Wass 2016).…”

“…This cutoff was chosen to represent a diagnostic proxy for suspected dyslexic reading difficulties, and the high cutoff chosen to minimize false-positive results when categorically defining children with reading difficulties. Behavioral-genetic modeling shows a substantial genetic influence on dyslexic-like reading difficulties as assessed with the scale (Brimo et al, 2021).…”

Genetic influences on neurodevelopmental disorders and their overlap with co-occurring conditions in childhood and adolescence: A meta-analysis

“…It is now well-established that NDDs often co-occur with one another, a phenomenon known as homotypic co-occurrence, and this points to a shared underlying liability between conditions 21,22 . Even in this instance, most genetic investigations have focused on examining the genetic correlations (i.e., the degree to which the same genetic variants contribute to the observed covariation between pairs of traits or disorders 23 ) between ASD and ADHD, which were found to be strongly phenotypically correlated (0.54) 24 .…”