Masking is a behaviour or strategy used by many Autistic people to appear non-Autistic and blend in with a neurotypical society. The goal of this observational study is to understand the relationship between masking, anorexia nervosa symptoms and brain structure in Autistic people. The main questions this study aims to answer are:

• Do Autistic individuals with anorexia nervosa show differences in structure or function of the brain relation to Autistic individuals without anorexia nervosa?
• Do Autistic individuals with anorexia nervosa display higher levels of masking than Autistic individuals without anorexia nervosa?
• Are there indeed relationships between levels of masking, anorexia nervosa symptoms and brain structure in Autistic people?

Researchers will compare Autistic people without anorexia nervosa to Autistic people with anorexia nervosa to see if there are differences between groups. Participants will:

• Complete a series of questionnaires focused on eating disorder symptoms, autistic traits, autistic masking and psychological well-being
• Undergo an MRI scan at the Aberdeen Royal Infirmary

Autism is a neurodevelopmental condition and presents as a distinct neurotype, characterised by a wide range of social and behavioural differences, including divergences in cognitive thinking and methods of communication. Autism shares significant behavioural features with restrictive eating disorders (EDs) such as anorexia nervosa (AN). Those with AN exhibit significantly elevated levels of Autistic characteristics, ranging between 2%-53%. Importantly, a characteristic shown by some Autistic people is the presence of masking, a term describing a strategy used by Autistic people, whether conscious or unconscious, to 'blend in' with neurotypical peers. While initially overlooked, it is now well-known that masking behaviour can produce detrimental effects on Autistic individuals' mental health. The presence of masking behaviour has been associated with increased levels of physical and mental exhaustion, anxiety/depression, and importantly, an increased presence of EDs.

The Eating Disorder and Autism Collaborative (EDAC) used an arts-based method called Photovoice to capture the experiences of Autistic individuals with lived/living experience of an ED. Participants commented on the how an ED can serve as a means to mask or camouflage within a neurotypical world (e.g., an Autistic person may use restrictive eating or excessive exercise as a means with which to 'fit in' with their peers). Magnetic resonance imaging (MRI) research can assist in understanding which regions of the brain are associated with masking behaviour, and whether there are differences in brain function/structure in Autistic individuals with versus without an ED.

Structural magnetic resonance imaging (MRI) research reports similarities in brain structure between those with AN and Autistic individuals, reporting differential structure of the amygdala, cerebellum, insula, cingulate cortex, as well as orbitofrontal and frontal cortex in both groups. Shared differences extend to neuroanatomical parameters essential for brain development and connectivity, such as cortical thickness and surface area. Further, there are no studies investigation structural correlates with masking behaviour, or distinct aspects of social camouflage such as masking, assimilation and compensation. Further research is necessary to disentangle the complex relationship between Autistic characteristics and symptomatology associated with restrictive EDs.

The investigators believe that by further understanding the brain structure and function associated with ED symptomatology and masking behaviour in Autistic individuals can assist with the development of novel or tailored interventions for EDs in this community.

Inclusion Criteria:

Healthy Autistic Individuals (Autistic Controls) must:

• Be aged 25-45 years
• Be Autistic (clinically diagnosed and/or have an Autism Quotient (AQ-10) score of ≥6)
• Be able to provide informed consent for the study
• Be able to read, understand and respond to questionnaires in English
• Have no history of an eating disorder
• Willing to have an MRI scan in Aberdeen

Autistic Individuals with anorexia nervosa must:

• Be aged 25-45 years
• Be Autistic (clinically diagnosed and/or have an AQ-10 score of ≥6)
• Be able to provide informed consent to the study
• Be able to read, understand and respond to questionnaires in English
• Have a diagnosis of anorexia nervosa or a body mass index of <18.5
• Willing to have an MRI scan in Aberdeen

Exclusion Criteria:

Individuals are not eligible for the study if they:

• Are aged <25 or >45 years
• Are not Autistic or not clinically diagnosed as Autistic and have an AQ-10 score of <6
• Are diagnosed with an eating disorder other than anorexia nervosa
• Have a history of brain injury (e.g., stroke)
• Be unable to provide informed consent for the study
• Have contraindications to MRI scanning, such has implantable cardiac devices
• Are unable to read, understand and respond to questionnaires in English
• As participants will need to consent to the study and complete questionnaires by themselves, individuals with intellectual disability will be excluded from this study

The population for this study consists of Autistic individuals who both present or do not present with acute anorexia nervosa. Study population will be recruited from Scotland, primarily the NHS Grampian region.

Our previous research with Autistic collaborators highlighted concerns regarding future use of their data for research that may harm Autistic identity. As such, IPD may only be available upon request from the principal investigators of this study and are subject to future ethical approval.