T113. CATEGORICAL AND DIMENSIONAL APPROACHES EXAMINING THE JOINT EFFECT OF AUTISM AND SCHIZOTYPAL PERSONALITY DISORDER ON SUSTAINED ATTENTION
Authors: Abu-Akel Ahmad , Philip Ruth C M , Lawrie Stephen M , Johnstone Eve C , Stanfield Andrew C 
Published: May 2020

Abstract

Background
Accumulating evidence for the co-occurrence Autism spectrum disorder (ASD) and schizotypal personality disorder (SPD) at both the diagnostic and symptom/trait levels raises important questions about the nature of their association and the effect of their co-occurrence on the individual’s phenotype and functional outcome. It has been recommend that informing etiological and phenotypic overlaps between ASD and schizophrenia spectrum disorders (SSD) would require the utilization of a dual-diagnosis cohort compared with two control groups, each singly diagnosed with ASD or SSD, and that the development of a multidimensional model for understanding the relationship between these two spectra would require cohorts to be described not solely by diagnosis, but also by using dimensional measures that cut across diagnostic boundaries. Research comparing adults with ASD and SPD, as well as the impact of their co-occurrence on outcomes is extremely limited. To fill in this gap, we investigated executive functioning in terms of response inhibition and sustained attention, candidate endophenotypes of both conditions, in adults with ASD, SPD, comorbid ASD and SPD, and neurotypical adults using both categorical and dimensional approaches.

Methods
A total of 88 adults (Mean Age ± SD = 37.54 ± 10.17): ASD (n = 26; m/f = 20/6); SPD (n = 20; m/f = 14/6); comorbid ASD and SPD (n=9; m/f =6/3) and neurotypicals (n=33; m/f =23/10) completed the Sustained Attention to Response Task (SART) in both its fixed and random forms.
Individuals with ASD had a DSM-IV diagnosis of either autism or Asperger Syndrome and met ASD cut-offs on the Autism Diagnostic Observational Schedule-Generic (ADOS-G). All individuals with SPD met DSM-IV criteria for SPD using the Structured Clinical Interview for DSM-IV Axis II Disorders (SCID-II). Individuals in the comorbid group met criteria for both ASD (determined by DSM-IV and the ADOS) and SPD (determined by the SCID-II). In addition, in both the clinical and healthy participants, positive and autistic symptom severity were assessed with the positive subscale of the Positive and Negative Syndrome Scale (PANSSpos) and the PANSS Autism Severity Score (PAUSS), respectively.

Results
Controlling for full scale IQ, working memory and medication dosage, group analyses revealed that the comorbid group committed fewer omission errors than the ASD group on the fixed SART, and fewer omission errors than the ASD and SPD groups on the random SART. The individual difference analyses revealed that the PANSSpos and PAUSS interactively reduced omission errors in both the fixed and random SARTs, as well as increased d’ scores, indicative of improved overall performance.

Discussion
Concurrent elevated levels of autistic and positive psychotic symptoms seem to be associated with improved sustained attention abilities. We propose that sustaining and switching attention may represent two poles of irregularities across the autism and schizotypal spectra, which appear to converge in a compensatory manner in the comorbid group. Our findings highlight the importance of investigating the concurrent effect of ASD and SPD at both the symptom and diagnostic levels, and the potential benefit of this research approach to understanding the underlying mechanisms of seemingly overlapping phenotypes.