Methodology

A significant strength of the study is that the authors adopted an active case-sampling approach, whereby they identified the autistic group through diagnostic assessment. This contrasts with a passive case-sampling approach, whereby the autistic and non-autistic groups are defined according to presence or absence of a pre-existing clinical diagnosis of autism on their medical records.^{Reference Tromans and Brugha5} The advantage of active case sampling is that it supports identification of autistic people whose autism previously remained unrecognised through routine clinical care. With passive case sampling, only diagnosed autistic people are identified; previous research demonstrates that many autistic adults are undiagnosed.^{Reference Brugha, Tyrer, Leaver, Lewis, Seaton and Morgan6} Furthermore, the characteristics of previously diagnosed autistic people, such as rates of co-occurring mental health conditions, may not necessarily be representative of all autistic people (i.e. undiagnosed plus diagnosed).

Nyrenius and colleagues conducted detailed clinical assessments to determine whether patients met diagnostic criteria for autism according to DSM-5.¹ However, they did cite difficulties in obtaining a parent-reported developmental history, with only 34% (n = 31) of the study population having returned these forms. This is a frequent challenge when attempting to obtain a developmental history from the parents of adult patients, as their parents may have died or they may be estranged from their parents, for example.^{Reference Lai and Baron-Cohen7}

However, it is important to acknowledge that the ‘merged-ASD group’ comprised not just adults meeting the full DSM-5 diagnostic criteria for autism spectrum disorder (n = 52), but also those meeting criteria for ‘subthreshold ASD’ (n = 11). Subthreshold ASD was defined as ‘meeting two out of three necessary A-criteria and at least two B-criteria of ASD according to the DSM-5’. Thus, the autistic group was not solely comprised of adults fully satisfying DSM-5 diagnostic criteria for autism spectrum disorder.

Mental health conditions

The authors report using an interview (the Mini-International Neuropsychiatric Interview version 7.0.1 with an ADHD supplement^{Reference Sheehan, Lecrubier, Sheehan, Amorim, Janavs and Weiller8}) and two tests (the Alcohol Use Disorders Identification Test^{Reference Saunders, Aasland, Babor, De la Fuente and Grant9} and the Drug Use Disorders Identification Test^{Reference Berman, Bergman, Palmstierna and Schlyter10}) to identify presence of mental health conditions in both the autistic and non-autistic groups, as well as identifying tic disorder via observation of tics during the interview assessment and/or participant self-report. However, such an approach also requires appreciation by assessing researchers that such conditions can present differently in autistic persons.

Interestingly, for most of the mental health conditions reported, there was no significant difference in rates between the autistic and non-autistic participant groups, with significant differences (Bonferroni-corrected alpha-level P = 0.0045) reported for only non-autistic neurodevelopmental disorders (attention-deficit hyperactivity disorder and/or tic disorders) and anxiety disorders. (The P-value was corrected because multiple comparisons were being made, which increased the risk of type 1 error, i.e. false positives.^{Reference Armstrong11}) This result may in part be related to the relatively small size of the study population, with the autistic and non-autistic groups comprising 63 and 27 participants respectively. However, it may also reflect the study population being psychiatric out-patients; although increased rates of mental health conditions in autistic people have been widely observed,^{Reference Lai, Kassee, Besney, Bonato, Hull and Mandy3} many such findings are from general population samples, and it is possible that rates among autistic and non-autistic adults utilising mental health services are more similar.

Psychosocial functioning

Global Assessment of Functioning (GAF)¹² scores were found to be significantly lower (P < 0.01) in the autistic group compared with their non-autistic peers. However, 26.7% of the variability in GAF scores in the autistic group was attributable to co-occurring psychiatric conditions. This suggests that much of the functional impairment reported by the autistic group is not directly related to their autism.

However, although the GAF is a widely used measure, its reliability and validity when used in adult psychiatric out-patient populations has been brought into question in previous studies.^{Reference Grootenboer, Giltay, van der Lem, van Veen, van der Wee and Zitman13}