Coeliac disease (CD) is an immune-mediated systemic disorder triggered by gluten in genetically predisposed patients. The only available treatment is a strict life long gluten-free diet (GFD), which has been linked to a reduced quality of life (QOL) and causes alterations in the gastrointestinal microbiome. Abnormal compositions of the microbiome are now recognized as factors in the pathogenesis of neuropsychological disorders via gut-brain-axis. The aim of this study was to assess the QOL and the mental performance of children and teenagers with CD and compare it to healthy controls (HC).

Methods: Children between the ages of 6 and 18 years with CD and age-and-sex-matched healthy controls (HC) filled in a questionnaire to assess QOL and performed the Flanker task, a standardized test to assess cognitive performance.

Between July 2020 and August 2021, all children aged between 6 and 18 years, under the care of the University Children's hospital of Basel and the Children's hospital of Aarau, Switzerland, diagnosed with CD according to the Guidelines for diagnosing CD of the European Society for Paediatric Gastroenterology, Hepatology and Nutrition, were informed about the study. Further inclusion criteria were a strict adherence to the diet, defined as a negative transglutaminase for at least one year before participation in the study. Exclusion criteria comprised a diagnosis made less than a year ago, the presence of other chronic diseases, including food allergies, and the intake of regular medication. CD patients and their parents were informed about the study during the regular appointment for a clinical and serological check-up. After obtaining their consent, patients received another appointment to participate in the study.

For every CD-patient an age-and-sex-matched healthy control was recruited. Exclusion criteria for healthy controls were chronic diseases, regular medication intake, food allergies or specific diets.

Firstly, all participants were asked to fill in the questionnaire to examine the QOL. 'Kidscreen52' was used, a standardized questionnaire containing 52 questions, developed to assess the subjective health and the psychological, mental, and social well-being of children and adolescents covering ten important aspects of life (physical well-being, psychological well-being, moods & emotions, self-perception, autonomy, parent relation & home life, financial resources, peers & social support, school environment, bullying). The answers to all questions were converted into numbers from one to five. In most subgroups, a higher number indicates a more positive answer, except for 'self-perception' (questions are like: 'do you doubt your appearance' etc.) and 'bullying', where a lower number indicates also less exposure to bullying. Participants were also asked to fill in the ISI (insomnia severety index), a 7-item self-report standardized questionnaire assessing the nature, severity, and impact of insomnia.

Participants completed a computerized Flanker task to assess cognitive performance. In this cognitive task, the target was flanked by non-target stimuli, which correspond either to the same directional response as the target (congruent flankers) or to the opposite response (incongruent flankers). In our child-friendly variant, participants were presented with five fish in a row and were asked to press the correct button according to the orientation of the target (central fish). Participants were instructed to respond as accurately and as quickly as possible. The two different conditions were presented with equal probability. Visual stimuli were shown for 200 ms against a black background, followed by a blank inter-trial period of random length between 900 and 1300 ms. Participants completed one practice block and two test blocks with 40 trials each. Flanker task is a reliable, well-recognized neuropsychological test for assessing executive function . Mean reaction times (on response-correct trials) and accuracy rates were calculated for congruent and incongruent trials.

To have consistency, the interviews and instructions for Flanker task were conducted by the same three students. Uncomplete patient data sets were excluded.

Inclusion Criteria:

• CD diagnosed according to European guidelines (ESPGHAN)
• only patients, who stick to a strict glutenfree diet (measured by transglutaminase for at least a year before participation in the study)

Exclusion Criteria: - any other chronic disease

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Children diagnosed with CD according to the Guidelines for diagnosing CD of the European Society for Paediatric Gastroenterology, Hepatology and Nutrition (ESPGHAN), were informed about the study. Further inclusion criteria were a strict adherence to the diet, defined as a negative transglutaminase for at least one year before participation in the study