Language-based risk factors in children with developmental dyslexia: A systematic review

Abstract

Background: Developmental dyslexia is a wide-ranging and persistent neurobiological disorder classified under specific learning disorders. The literature widely recognises the multifactorial nature of developmental dyslexia, specifically the language-related origin. Objectives: The current review systematically identified and synthesised possible language-based risk factors associated with developmental dyslexia in children (age one to three and four to ten years) and determined the level of evidence associated with these risk factors. The review aimed to identify individualised risk factors in children with developmental dyslexia to promote optimal neurodevelopmental outcomes. Method: Four relevant databases were searched from January 2002 until December 2018. A hand search of the included articles’ reference lists was also performed to identify any relevant publication. The language-based risk factors in children with developmental dyslexia in 48 publications were studied. Results: All language components are compromised to some degree in children with developmental dyslexia at specific ages. These results indicate the intricacy of language, but also emphasise that developmental dyslexia should be considered on a continuum and not as an absolute disorder. Only a few studies investigated language-based risk factors in participants five years and younger. Phonological-based risk factors were the most reported language component and comprise of risk factors within phonological awareness, rapid automized naming, and working memory. The second language component entailed morphology. Several inflectional and derivational morphological risk factors, as well as risk factors within syntactic processing, were acknowledged. Compromised receptive and expressive vocabulary knowledge, semantic processing, and fluency were identified as risk factors for the language component of semantics. The final component of language entailed pragmatics. Unfortunately, a limited amount of evidence is available in this regard. However, the evidence available confirmed poor linguistic pragmatics as a risk factor in children with developmental dyslexia. Conclusion: These language components are interrelated and should be viewed holistically as risk factors for developmental dyslexia to promote earlier identification.