Comorbidity Between Reading Disorder and Specific Language Impairment: In Search of Distinct Cognitive Profiles

• In Event: 2-103 - Comorbidity in Specific Developmental Disorders: Examining Prevalence Rates, Cognitive Causes, and Implications for Treatment

Integrative Statement

Reading disorder (RD) and Specific Language Impairment (SLI) are among the most prevalent developmental disorders and show high comorbidity rates with up to 50%. Although poor phonological processing has been proposed as a core deficit underlying both disorders, the specific cognitive profiles leading to isolated or combined manifestations of RD and SLI are not well understood. Assessing cognitive deficits prior to the manifestation of the disorders in at-risk children can reveal their cognitive causes. Such retrospective longitudinal studies allow disentangling cause from effect and are thus especially suitable for etiology research and may also help to understand the cognitive underpinnings of comorbidity.
Testing a multiple-cognitive deficit model in a retrospective longitudinal design, it was anticipated that RD and SLI share a deficit in phonological processing. It was further hypothesized that RD is additionally caused by etiological factors outside the phonological domain. Lastly, it was assumed that the cognitive profile of the comorbid group is best described by the additive combination of the two single disorders.
Overall, 107 at-risk children (girls: 55%; Mage = 68.80 months; SDage = 3.72) were assessed on domain-specific phonological skills and domain-general cognitive abilities prior to school entry and were then reassessed on reading and language performance at the end of Grade 2. Based on their Grade 2 performance, children were categorized into four groups: RD-only (n = 30; reading < 16th percentile), SLI-only (n = 19; language < 16th percentile), RD+SLI (n = 18; reading and language < 16th percentile), and a group with neither disorder (n = 40; reading and language ≥ 16th percentile). To examine early distinct and overlapping cognitive profiles associated with later RD- or SLI-status, 2 (RD: yes versus no) × 2 (SLI: yes versus no)-factorial (M)ANOVAs were conducted on the phonological and cognitive measures assessed prior to school entry.
There was a significant main effect of SLI (but not RD) on most phonological measures: Specifically, children who developed SLI by Grade 2 were characterized by poor phonological awareness, poor phonological short-term memory and low performance in sentence recall in kindergarten. In contrast, children with later RD performed poorly in the naming speed task only. In addition, there was a significant main effect of RD (but not SLI) on domain-general measures: Children who developed RD by Grade 2 showed poor executive functions and low self-regulation prior to school entry. The RDxSLI-interaction was not significant suggesting an additive profile for the comorbid group. A discriminant analysis further showed that a great proportion of group membership in Grade 2 could be correctly predicted based on the cognitive profiles in kindergarten.
Given the results, cognitive deficits may be attributed to RD although they might, in fact, be caused by a subsample of children with comorbid SLI (and vice versa), if RD-studies overlook the possibility of additional oral language deficits in their sample (and vice versa). Comorbidity may thus account for some of the heterogeneous results reported in the literature on the cognitive correlates of RD and of SLI.

Authors

• Janin Brandenburg, German Institute for International Educational Research (DIPF)
  Presenting Author

• Sina Simone Huschka, German Institute for International Educational Research (DIPF)
  Non-Presenting Author

• Marcus Hasselhorn, German Institute for International Educational Research (DIPF)
  Non-Presenting Author