Adaptive Functioning on the Borderlands of the Autism Spectrum

Background: Autism spectrum disorders (ASDs) are considered to be dimensional, sitting at the extreme end of a continuum that extends throughout the general population. As such, there are individuals with elevated autistic traits who do not meet criteria for an ASD. It is likely that, under current proposals for ASD in DSM-5, the diagnostic threshold will be raised, thus excluding from the autism spectrum some individuals who currently meet criteria for Asperger’s syndrome and pervasive developmental disorder not otherwise specified (PDD-NOS). This raises the question of where the threshold for ASD diagnosis should be set. One approach to evaluating the validity and utility of a diagnostic threshold is to test how well it captures people with high levels of functional impairment and excludes individuals who are not seriously functionally impaired.

Objectives: To investigate levels of adaptive functioning across the range of autistic presentations, to test how well current diagnostic thresholds distinguish between individuals with and without clinically severe levels of adaptive dysfunction.

Methods: Seventy-two young people (mean age = 11.03 years), referred for assessment at a specialist autism spectrum disorder (ASD) clinic were administered the Vinelands Adaptive Behaviour Scales (VABS); the parent-report 3Di; the Autism Diagnostic Observation Schedule (ADOS); Wechsler intelligence tests; and the Repetitive Behaviour Scale-Revised. Participants were classified according to DSM-IV-TR diagnosis, and those below threshold were included if they met AGRE criteria for ‘broad spectrum’ difficulties. Initially these groups were compared on measures of adaptive function. Correlational and regression models were then used to investigate relationships between IQ, autistic symptomatology and adaptive functioning.

Results: Adaptive functioning was impaired for the great majority of participants (88.9% scored within the VABS ‘low’ and ‘moderately low’ range). The proportion of children with impaired adaptive function did not differ significantly (p>.43) in individuals with autism (100% with impaired adaptive function), Asperger’s syndrome (89%), PDD-NOS (84%) and sub-threshold autistic traits (92%). Individuals with sub-threshold, ‘broad spectrum’ autistic difficulties experienced adaptive function difficulties that were as severe as those with autism. In regression models, only IQ and reciprocal social interaction impairments were predictive of adaptive functioning difficulties in this clinical sample.

Conclusions: Young people presenting at a social-communication clinic with partial and sub-threshold autistic presentations show significant and severe adaptive functioning difficulties. These are as severe and widespread as disabilities found in children with full PDD diagnoses, namely Autism and Asperger’s syndrome. This suggests that current diagnostic thresholds may be set too high to adequately capture all individuals whose autistic traits engender significant disability. Furthermore, plans to make ASD diagnosis more stringent in DSM-5 are likely to exclude children with clinically significant autistic difficulties from the support and treatment that comes with an ASD diagnosis.