Comparison of Children with Autism Spectrum Disorders and Developmental Language Disorders on Measures of Language Impairment

Background: There are areas of overlap between autism spectrum disorders (ASD) and developmental language disorders (DLD) that pose challenges for differential diagnosis. One such area is language impairment. There have been varying reports on the types of language issues and percentage of children with ASD who show them, as well as varying positions with respect to the relationship between ASD and DLD. High functioning verbal children with autism have been reported to show no deficits in phonology, syntax, or lexical knowledge, and problems primarily in pragmatics; others have identified deficits in structural language and the same pattern of impairments as in DLD, pointing the way to a possible common genetic etiology for some (Kjelgaard and Tager-Flusberg, 2001; Joseph, et al., 2004). Still others think of there being multiple subtypes of language impairments in ASD (Rapin, et al., 2009).  Clearly, a more detailed characterization of comparative language impairments in ASD and DLD is needed, with particular attention to heterogeneity in ASD.

Objectives: Objective is to document incidence of language impairment in a well-characterized group of high functioning verbal children with ASD and to compare their language issues with those of an equally well-characterized group of children with DLD.

Methods: Children, ages 4-8, were given a comprehensive battery of language and neurocognitive measures. Classification into the ASD group (N=47) utilized the ADOS revised algorithm, the Social Communication Questionnaire, and DSM-IV-TR-based clinical consensus diagnosis of ASD. Classification into the DLD group (N=22) utilized Tomblin’s Epi-SLI criteria or a CELF index score at -1 SD plus a spontaneous language measure at -1 SD, and DSM-IV-TR-based diagnosis.  Stringent exclusion criteria were applied, such as bilinguality, neurological condition, metabolic or genetic disorder, severe intelligibility impairment.

Results: (1) 66% of the ASD group met criteria for language impairment (“ASD+DLD”, N=31/47). (2) For most EpiSLI domains, more children with ASD+DLD than with DLD exceeded cut-off scores. (3) The ASD+DLD and “ASD-DLD” (i.e., children in the ASD group not meeting criteria for language impairment) subgroups differed on ADOS revised scores but had nearly identical SCQ scores. (4) The ASD+DLD, ASD-DLD, and DLD groups had equally slow Processing Speed scores. (5) Differential clinical markers: Both ASD subgroups significantly outperformed the DLD group on the NRT and on Expressive Vocabulary, while the ASD+DLD subgroup performed significantly worse than the DLD group on narrative comprehension and on the Receptive Language Index.

Conclusions: This ASD group, confined to verbal children with high functioning autism and meeting stringent criteria, is surprisingly heterogeneous. Also, even in this group, the percentage of children with language impairments is high. However, the pattern of language impairment in ASD+DLD is different from that of DLD. This does not imply, however, nor exclude the possibility that there may be a subtype within the ASD+DLD group that does have a pattern of impairment similar to DLD or to a DLD subtype. The question of distinctive subtypes in both ASD and DLD – and areas of both overlap and essential differences – beckons for further disclosure.