Asperger Syndrome in Adults: Evidence for the Validity of Contemporary Screens

Background:  Knowledge of Asperger Syndrome (AS) in children has increased substantially in recent years; yet, information on diagnosis in adults is limited.  Adult assessment may be difficult for various reasons: early developmental history may be unobtainable; co-existing conditions may be present; and/or experienced and knowledgeable clinicians may be unavailable.  Tests to assist in diagnosing adult AS exist, but they have limitations: (1) many tests were created for use with children; (2) information on reliability and validity of test scores are often unavailable; and (3) test developers do not always obtain independent confirmation that their participants actually have AS.  Thus, the usefulness of tests for identifying AS in adults remains questionable and may result in inaccurate diagnoses.

Objectives:   Given the above, the goals for our current study were to augment the existing information for several tests of adult AS to determine: (1) how well these instruments discriminate between groups of people with autism spectrum disorders (ASD) (discriminant validity); (2) if the instruments are strongly related to other tests for AS/ASD (convergent validity); and (3) if the instruments differ from tests of other conditions (divergent validity). Further, we examined the accuracy of AS diagnoses when instruments are used individually or in combination.

Methods:   In a pilot study, we recruited adults (aged 18+ years) with AS and IQ-, gender-, and age-matched controls in each of three groups – high functioning autism (HFA), attention deficit hyperactivity disorder (ADHD), and typically developing.  These groups were chosen to evaluate the sensitivity of existing measures for discriminating between similar (HFA), overlapping (ADHD), and distinct (typically developing) groups.  All clinical participants were diagnosed by a clinician prior to their participation and had a verbal IQ ≥ 85.  Participants completed various AS screening/diagnostic measures [e.g., Krug Asperger Disorder Index (KADI); Gilliam Asperger’s Disorder Scale (GADS); The Adult Asperger Assessment (AAA); Asperger Syndrome Diagnostic Interview (ASDI); and Ritvo Austim Asperger Diagnostic Scale- Revised (RAADS-R)] and other tests included to measure convergent and divergent validity.

Results: Findings are preliminary, however, they do indicate that some instruments are better at correctly identifying and discriminating amongst subgroups and that combining selected instruments improves classification rates.

Conclusions:   Families and individuals affected by a late diagnosis of AS experience frustrations and difficulties.   Many clinicians feel inadequately prepared to assess adults on the spectrum, as resources for late diagnosis are limited.  Thus, it is essential that clinicians feel competent to address the unique diagnostic needs of adults suspected of having AS.  The results from our study provide a step towards improving this situation at a clinical level, and we anticipate that this will likewise positively impact individuals and families by enabling accurate diagnosis and, thus, access to appropriate supports and treatment.  Our findings are essential to informing understanding of AS in adults and improving clinical assessment and diagnosis of AS.