Literature regarding white matter differences in children with developmental language disorder (DLD) has shown inconsistent results. Furthermore, relevance of neuroanatomical differences between typically developing children and children with DLD to language function has scarcely been investigated. Therefore, this study investigated white matter differences in children with DLD using fixel-based analysis, deriving fiber-specific metrics with increased biological specificity. Relations between fixel-based metrics showing group differences and behaviour were investigated for several language measures. Method. Dorsal (e.g., arcuate fasciculus) and ventral (e.g., uncinate fasciculus) language tracts and white matter of the cerebellar peduncles were modelled in 21 children with DLD and compared to that of 21 typically developing children between eight and 13 years of age. Children also completed an extensive language assessment, including overall language performance, vocabulary and word learning. Fixel-based metrics of the informative tracts (> 50 significant fixels in comparisons between groups) were regressed with the different language measures.
Results. Children with DLD showed differences in fiber (density) cross-section in the uncinate, arcuate and superior longitudinal fasciculi, which were associated with overall language and/or vocabulary performance. Further, fixel metrics of the dorsal tracts were related to immediate recall of learned words. Discussion and conclusion. Our findings suggest that white matter differences in DLD could be associated with morphological differences in fiber bundle diameter or size. Further, atypical structural white matter properties may contribute to the observed language impairments. Our findings suggest that fixel-based analysis is a promising technique to detect fiber-specific differences in children with DLD.