This study set out to investigate autistic traits in individuals with AN. Individuals with AN scored significantly higher on the AQ-10 than typical control participants. Furthermore, analysis of responses to individual items of this scale revealed significant differences for the majority of questions. This supports the hypothesis that women with anorexia possess a greater number of autistic traits than typical women and replicates the findings of previous studies [4, 44]. In addition, this study goes beyond the existing literature as the first study using the AQ-10 in a population with AN. Using the clinical cut-off recommended by the scale’s authors, more than a quarter of the AN group obtained a score high enough to warrant a referral to an ASC assessment service (referrals were made in these instances), closely reflecting the frequency of patients meeting full clinical criteria in an adult AN population [13]. In contrast, less than 2% of the control participants scored over the cut-off point.

Following on from these results, an exploratory analysis of how these elevated levels of autistic traits were related with other self-reported symptoms in the AN group revealed a strong correlation with mood, including both anxiety and depression, and the ability to maintain close relationships. Regression analyses showed a predictive role of the AQ-10 total score, indicating that higher levels of autistic traits are associated with feeling anxious and depressed and that this might explain difficulties in interpersonal interactions for people with AN [1]. It is interesting to note that significant correlations were not observed between autistic traits and eating disorder symptoms. It is important to consider whether the AQ-10 is in fact measuring mood symptoms rather than autistic traits, a situation that would threaten the validity of this instrument. Examining the individual items reveals that only certain questions may directly relate to emotional problems (for example, difficulty multitasking and coping with interruptions relates to poor concentration) with a greater number tapping into other cognitive or socio-emotional domains. This would suggest that symptoms of anxiety and depression might increase scores slightly; however, the range of questions appears to reflect typical autistic traits and therefore have good face validity. How can the significantly higher AQ-10 scores in individuals with AN be reconciled with a failure to demonstrate a direct link between autistic traits and disordered eating? It could be speculated that autistic traits exacerbate ‘maintaining factors’ for eating disorder, such as cognitive rigidity, low mood, low motivation or a lack of social skill, with the latter two factors relating to the significant correlations reported here, rather than directly causing the eating disorder behaviours. In a recent study, eating disorders (AN and bulimia nervosa), anxiety disorders and depression accounted for a large portion of difficulties with social functioning [53]. Although the outcome measure was somewhat different in this study, it suggests that eating symptoms, as well as mood, are expected to be associated with autistic traits falling within the social domain.

Nevertheless, the current study along with previous research indicates a significant trend: people with AN are more likely to show autistic traits. Several factors might play a part in this. For example, starvation has been shown to reduce the quality of interpersonal relationships, interest in other people, and libido [55]. Secondly, a detailed assessment of the items on the AQ-10 revealed that seven out of the ten items discriminated between patients with AN and control participants. These items tap into problems with ‘bigger picture’ (global) thinking (item 1, 2 and 7); inflexibility of thinking (item 3 and 4) and problems with social interactions (item 5 and 10).

In the adult literature, the presence of difficulties in these three domains in the AN population has received empirical and experimental support. For example, problems with abstract thinking are reported in a systematic review conducted by Lopez et al. [36] and have been shown to be experienced by AN patients in experimental studies [38, 39]. In addition, problems with flexibility of thinking are reported in the systematic review [33] and large data-based studies of Tchanturia et al. [31, 32]. It is also notable that social anhedonia [1] and problems with social cognition [5, 20] have been widely reported in the literature.

The items that did not significantly discriminate between patients with AN and controls appear to tap into theory of mind abilities, including difficulty reading faces and working out characters’ intentions. Despite the literature described (for example, [14, 20–22]), this is in accordance with a psychometric study reporting that both AN and ASC groups demonstrated a need for sameness; however, other core features of autism, such as difficulty empathizing, were not seen in the AN group [56].

Limitations

A main aim of the study was to test the AQ-10 in an eating disordered population; therefore, the primary outcomes were self-reported. For future studies, additional clinical interviews and experimental (performance-based task) designs could improve the validity and reliability of findings. The AN group consisted of inpatients, daycare patients and outpatients; this may have introduced heterogeneity into the data, owing to varying levels of illness severity. However, all patients met the DSM–IV criteria for AN and were receiving treatment. Finally, it was not possible to recruit a recovered AN group; this may be useful in exploring whether elevated levels of autistic traits are present in the recovered form of this eating disorder diagnostic group as well as the acute state. This is an important area to investigate, as a recent study has reported that difficulties with social cognition and communication were less prominent in a recovered AN group [57]. This raises the possibility that high scores on measures of autistic traits could be, in part, a consequence rather than a cause of AN.

Clinical implications

Exploring links between ASC and AN can provide important insights into the aetiology of both conditions. In terms of clinical implications, women are a challenging group for ASC professionals to diagnose [58], while AN is the most challenging condition to treat on the eating disorder spectrum [59]. Brief screening instruments, such as the AQ-10, provide helpful and easy tools that facilitate better understanding of the patient’s problems and may lead to better tailoring of intervention. It is possible that women with AN who have high scores on the AQ-10 might benefit more from cognitive therapies than from other psychological or pharmacological treatments that do not directly address problems with set-shifting, bigger picture thinking or socio-emotional deficits. Existing module-based treatment packages (for example, cognitive remediation therapy [60, 61] and cognitive remediation and emotion skills therapy [62]) provide targeted interventions with which to address ASC symptoms in a population with AN. Further research is required to investigate the effectiveness of these intervention packages in relation to ASC symptomatology.