Investigating the prevalence and comorbidity of attention deficit hyperactivity disorder and developmental dyslexia in learners in a South African practice

Abstract

Background: Dyslexia and attention deficit hyperactivity disorder (ADHD) are marked comorbid neurodevelopmental disorders with an estimated bidirectional comorbidity of 25% – 40%. Previous international studies have identified strong hereditary and neurological overlap between these disorders, but the comorbidity of these developmental disorders in a South African practice has not yet been explored. Methods: This retrospective study aimed to investigate the co-existence of ADHD and the specific learning disorder (SLD) related to reading known as developmental dyslexia (DD). Additionally, the study sought to determine possible correlations between the overlapping diagnostic factors of the two developmental disorders. The study database consisted of 847 learners ranging from 8 to 18 years of age. Study data were obtained through a parent questionnaire regarding scholastic difficulties as well as prior ADHD diagnosis and/or treatment. A comprehensive psychometric assessment of DD was conducted on each participant in the first language of educational instruction, that is English or Afrikaans, to establish a direct dyslexia diagnosis as inclusion criterion. Results: Of the 847 participants analysed in this study, 38.6% presented with a co-existing diagnosis of both ADHD and DD. However, there was no evidence of statistically significant interdependency between overlapping diagnostic factors of these two disorders. Conclusions: The zero-correlations in the mentioned areas may indicate an overlap of shared symptoms rather than of distinctive diagnostic approaches.