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Introduction
A growing body of literature indicates a link between anorexia nervosa (AN) and autism spectrum disorder (ASD). A systematic review of the prevalence of ASD in AN reported a mean rate of 23% (Huke et al. 2013); however, six of the included studies came from the same Swedish community sample and this line of research is ongoing (Nielsen et al. 2015). There are also similarities in cognitive style between AN and ASD (Gillberg et al. 2010; Oldershaw et al. 2011; Courty et al. 2013; Tchanturia et al. 2013a ) reported in the literature. Although elevated levels of autistic traits have consistently been found within AN populations (Baron-Cohen et al. 2013; Tchanturia et al. 2013b ; Huke et al. 2014; Rhind et al. 2014; Westwood et al. 2016) it is not known whether the presence of these traits represents a shared, underlying mechanism (Zucker et al. 2007; Odent, 2010; Allely, 2013) or whether individuals with AN come to resemble those with ASD due to the chronic, starved state associated with the disorder (Pellicano & Hiller, 2013; Treasure, 2013). Direct comparison of the seemingly shared traits, as well as systematic exploration of these traits across stages of illness, e.g. childhood and adulthood, will be essential to understanding the extent to which these traits may be shared mechanisms in both AN and ASD.
Interest in the potential relationship between AN and ASD has led to examination of cognitive traits, believed to underpin ASD in AN. While some traits associated with ASD, such as emotional theory of mind, have been found to reduce in recovered AN groups (Oldershaw et al. 2010), other traits including difficulties with set-shifting, or flexible thinking, appear to persist after weight gain (Tchanturia et al. 2004; Gillberg et al. 2010; Danner et al. 2012; Lindner et al. 2014). Recent reports suggest that set-shifting inefficiencies are present in children with AN who have had a relatively short duration of illness (Lang et al. 2015a ) and relatives with AN (Holliday et al. 2005; Roberts et al. 2010; Lang et al. 2015b ). Conversely, fasting in healthy controls (HCs) has been found to reduce set-shifting test performance, suggesting that starvation may exacerbate underlying difficulties in this domain (Bolton et al....