Developmental Language Disorder and Developmental Dyslexia: Rethinking Categorical Boundaries Through a Dimensional Language–Literacy Framework

Abstract

Developmental Language Disorder (DLD) and developmental dyslexia are among the most prevalent neurodevelopmental disorders affecting children’s language, literacy, academic achievement, and social participation. Although traditionally conceptualised as distinct disorders of oral and written language, respectively, increasing evidence suggests substantial overlap in their underlying developmental mechanisms while preserving distinguishable clinical phenotypes. This critical narrative review synthesises evidence from epidemiological, longitudinal, cognitive–linguistic, behavioural genetic, and clinical studies examining the relationship between DLD and developmental dyslexia. Particular attention is given to prevalence, comorbidity, shared risk factors, developmental trajectories, and the implications of categorical versus dimensional models for clinical assessment and intervention. The evidence indicates that DLD and developmental dyslexia share multiple cognitive and linguistic liabilities, including weaknesses in phonological processing, verbal memory, processing efficiency, and broader oral language abilities. These vulnerabilities interact with genetic, environmental, educational, and orthographic influences, producing heterogeneous developmental profiles and frequent comorbidity. At the same time, each disorder retains characteristic clinical features that justify their continued diagnostic distinction. The available evidence supports a hybrid conceptualisation in which DLD and developmental dyslexia are viewed as distinct but partially overlapping neurodevelopmental disorders within a multidimensional language–literacy framework. Building on previous work concerning diagnostic differentiation, comorbidity, and shared developmental mechanisms, this review integrates epidemiological, developmental, cognitive–linguistic, genetic, cross-linguistic, and clinical evidence within a clinically oriented two-dimensional language–literacy framework intended to generate testable hypotheses and inform future research on assessment and intervention.