Early speech-language impairment and risk for written language disorder: a population-based study.

Speech-language problems are common among children. The prevalence of speech sound impairment in children ranges from 1.3% to 12.6% depending on age and criteria used, and estimates of prevalence of specific language impairment (SLI) range from 2% to 19%.1 Written language disorder (WLD) and reading disorder (RD) are subtypes of language-based learning disability (LLD) that are also common in childhood. In two population-based studies, the cumulative incidence of RD ranged from 5.3% to 11.8% and the cumulative incidence for WLD ranged from 6.9% to 14.7% depending on criteria used. 2,3 The relationship between speech-language impairment (S/LI) and RD has been well established, with long term implications beyond difficulty learning to read.4–7 Tomblin, et al. not only found a strong correlation between spoken language skills and reading, but their data suggested an association that leads from oral language difficulties to academic difficulties, which then play a role in the development of behavioral outcomes in some children. In a systematic review of the literature, McCormack et al. found that early history of speech impairment (which included some children with both speech and language impairment) was associated with a broad range of later difficulties including academic skills in reading, writing, calculating, focused attention and thinking, and social outcomes including social and family relationships and job-related skills. The relationship between S/LI and WLD has been less well studied, but there is a growing body of research exploring the relationship between speech-language skills and written language impairment. 8–11 Puranik & Lonigan found that as early as preschool, children with oral language impairment were significantly delayed relative to peers with typical development in their early writing-related skills. Several researchers found that children with S/LI produced written narratives that were less complex than either age-matched or language-matched peers.8–9 Additional studies suggest that speech problems and/or oral language impairment can have an adverse impact on later development of written language skills and an association with more general academic and social struggles.12–14 This study adds to the current base of knowledge by examining co-occurrence of S/LI and WLD in an unbiased, population-based, non-referred sample. There is evidence of familial transmission of S/LI and RD, and it seems likely that genetic factors influence vulnerability for WLD as well. However, distinct loci have yet to be identified for specific disorders, in part because these difficulties are understood to be multifactorial in nature.15–16 In this paper, we will use the designation “S/LI” to refer to children presenting with speech and/or language impairment, that is, speech impairment, specific language impairment, or both together. Because S/LI may be one early indicator of WLD, understanding the relationship between these disorders can help to determine to what degree S/LI should be considered a risk factor in children who are not yet reading and writing. Early identification of children with S/LI and early intervention for children at risk for WLD could potentially moderate the severity of these problems. The availability of records from a population-based birth cohort with research-identified WLD2 provided an opportunity to study the co-occurrence of S/LI and WLD. The primary purposes of this study were to: (1) compare risk for WLD among children with S/LI and children without S/LI; and (2) compare the risk for WLD associated with S/LI between boys and girls. Finally, the association between WLD and SLI was examined separately for children who had WLD without RD versus WLD with RD.