Profiles of structural language and nonverbal intellectual abilities in verbal autistic adults

Background: A diagnosis of autism includes the specification of any accompanying language impairment (LI) and Disorders of Intellectual Development (DID). The International Classification of Diseases (ICD-11) mentions the existence of four different profiles for verbal autistic individuals, resulting from the logical combinations of presence and absence of LI and DID. While these profiles have been identified in autistic children, equivalent evidence is lacking for adults, as studies on this population are quantitatively and qualitatively limited. Language tasks are generally ill-adapted to autistic adults and individuals with DID are rarely integrated into experimental cohorts. This study means to fill this gap by proposing a systematic investigation of structural language and nonverbal intellectual abilities (NVIQ) in autistic adults across the whole verbal spectrum based on explicitly motivated measures. Methods: For structural language, the adult adaptation of autism-friendly nonword and sentence repetition tasks shown to be sensitive to LI were selected; for NVIQ, Block Design and Matrix Reasoning of the WAIS-IV were employed. These tasks were administered to 48 autistic adults aged 18-56 years and to 50 age-matched controls. Results: Cluster analysis revealed three distinct profiles: two homogeneous (intact language with high NVIQ and LI with low NVIQ) and one displaying discrepant abilities, including normal language with low NVIQ. Conversely, the LI with average/high NVIQ profile was not found. Conclusions: Profiles in adulthood seem more homogeneous than in childhood. One hypothesis is that cognitive changes occur during development that reduce ability discrepancy, such as severe LI contributing to decreasing nonverbal abilities over time.