Introduction: Various studies have shown a high association between gender incongruence (GI) and mental disorders, and a higher presence of GI in certain populations such as autism spectrum disorder. The scientific literature on GI in people with intellectual developmental disorder (IDD) is very sparse, no data on the effects of gender-affirming hormone therapy and gender-affirming surgery are available.

Aims: We report the first case of an individual with GI and IDD and comorbid psychiatric disorders who underwent gender-affirming treatments, with a largely positive outcome.

Methods: We describe the diagnostic assessment and the course of treatment of a transgender man, assigned female at birth, with a mild IDD (IQ 53) and bipolar disorder, who benefited from gender-affirming hormone therapy, followed by gender-affirming surgery such as torsoplasty with bilateral mastectomy, hysterectomy with oophorectomy, colpectomy, and proximal urethroplasty and finally phalloplasty. He also benefited from appropriate psychological support and from treatments to stabilize psychiatric disorders.

Results: Two years after the phalloplasty, he reports complete disappearance of GI. Psychiatric symptoms have reduced, in terms of anxiety and mood swings, to the point where psychiatric hospitalization were no longer necessary since torsoplasty with bilateral mastectomy. His social functioning has also improved.

Conclusion: This case report provides a clear focus on the importance of multidisciplinary work between IDD and GI specialists to evaluate and manage GI in individuals with IDD. It addresses the complexity of gender identity exploration and expression for individuals with IDD and brings attention to their vulnerability. This case report offers limited exploration of practical solutions or interventions and does not provide detailed treatments strategies. Given the complexity of this case report, which involves both IDD and bipolar disorder, it is challenging to draw generalizations or definitive conclusions.