The Concept of Dimensionality, Applied to Proposed DSM-5 Criteria for Autism Spectrum Disorder

Background: A question that is pertinent to the conceptual background underlying revisions to the definition of autistic disorders in DSM-5 concerns the extent to which we should regard this heterogeneous set of conditions as representing multidimensional traits that vary in severity relatively independent of one another. DSM-5 goes some way to reflecting a widespread view that dimensional descriptors are a more appropriate way of reflecting individual differences in symptom severity and general impairment. The implications of employing a dimensional framework for diagnosis, compared to a categorical one, are profound and could impact upon both the provision of clinical care and strategies for neurocognitive and genomic research.

Objectives: We aimed to evaluate the validity of proposed DSM-5 criteria for autism spectrum disorder (ASD).

Methods: We analyzed symptoms from 14,744 siblings (8,911 ASD and 5,863 non-ASD) included in a national registry, the Interactive Autism Network. Youth 2 to 18 years of age were included if at least one child in the family was diagnosed with ASD. Caregivers reported symptoms using the Social Responsiveness Scale and the Social Communication Questionnaire.  The structure of autism symptoms was examined using taxometric procedures and latent variable models that included categories, dimensions, or hybrid models specifying categories and subdimensions. Diagnostic efficiency statistics evaluated DSM-IV-TR, the proposed DSM-5 algorithm, alterations of the DSM-5 algorithm in identifying ASD.

Results: We found a hybrid model that included both a category (ASD versus non-ASD) and two symptom dimensions (social communication/interaction and restricted/repetitive behaviors) was more parsimonious than all other models, and replicated across measures, subsamples, and taxometric procedures. Empirical classifications implied a broad ASD category distinct from non-ASD. DSM-5 criteria had superior specificity relative to DSM-IV-TR criteria (0.97 versus 0.86); however sensitivity was lower (0.81 versus 0.95). Relaxing DSM-5 criteria by requiring one less symptom criterion increased sensitivity (0.93 versus 0.81), with minimal reduction in specificity (0.95 versus 0.97). Including hypo- and hyper-sensory sensitivities and unusual sensory interests increased sensitivity to ASD without altering specificity.

Conclusions: Our results supported the validity of proposed DSM-5 criteria for ASD as provided in Phase I Field Trials criteria. Increased specificity of DSM-5 relative to DSM-IV-TR may reduce false positive diagnoses, a particularly relevant consideration for low base rate clinical settings. We recommend that Phase II testing of DSM-5 should consider a relaxed algorithm, without which as many as 12% of ASD-affected individuals, particularly high functioning cases and females, will be missed. Relaxed DSM-5 criteria may improve identification of ASD, decreasing societal costs through appropriate early diagnosis and maximizing intervention resources.