A case of celiac disease carrying the half DQ2 variant with a variety of psychiatric manifestations.

Background: Celiac disease (CD) is an autoimmune-mediated systemic disorder triggered by the ingestion of gluten. While it typically presents with gastrointestinal symptoms, it is also associated with various neuropsychiatric manifestations, including depression, migraine, developmental disorders, and epilepsy. In Asia, particularly in Japan, CD remains underdiagnosed, potentially delaying appropriate diagnosis and treatment for early intervention. Case Presentation: We report the case of a 16-year-old girl who presented with long-standing behavioral issues, including repeated theft and rule violations since elementary school. She was diagnosed with attention-deficit/hyperactivity disorder (ADHD), conduct disorder, and oppositional defiant disorder, but responded poorly to psychiatric treatment. In light of her coexisting physical symptoms, including chronic gastrointestinal complaints and unexplained laboratory abnormalities, further evaluation, including a duodenal biopsy, was conducted. The diagnosis of CD was confirmed, and a gluten-free diet was initiated. Following dietary intervention, both her psychiatric and physical symptoms improved significantly, and no recurrence was observed during follow-up. Conclusion: This case highlights the importance of considering CD as a differential diagnosis in adolescents with treatment-resistant psychiatric symptoms, especially when accompanied by physical signs suggestive of systemic disease. Early recognition and intervention with a gluten-free diet may improve both psychiatric and physical outcomes.