Biological studies of transgender identity: A critical review

Introduction: There is increasing public and research interest in transgender people and communities. Coupled with this interest is a renewed pursuit of research into the possible biological origins of transgender identity. In this review, we critically examine the biological literature which explores the etiology of transgender identity, including endocrinological, behavioral, genetic, and neuroimaging studies, with the goal of identifying key trends in this literature, limitations, critical gaps, and future directions. Methods: We searched the Pubmed database for peer reviewed original experimental research conducted since 1990, using a combination of six transgender identity-related search terms and 18 topic search terms. Results: A total of 102 articles across the disciplines of endocrinology, genetics, cognitive function, and neuroanatomy met our review criteria. Most studies were conducted at gender identity clinics. Several approaches yielded compelling results, but where replication has been attempted, results have varied. We identified several issues in experimental design and/or interpretation that might account for this inconsistency. Conclusion: A number of research studies have investigated biological factors that could potentially contribute to transgender identity, but results often contradict each other. Interpretation of etiological studies of transgender identity can be misunderstood and/or misused by media, politicians, and care providers, placing transgender people at risk. We question the utility of etiological studies in clinical care, given that transgender identity is not pathological. When etiological studies are undertaken, we recommend new, inclusive designs for a rigorous and compassionate approach to scientific practice in the service of transgender communities and the providers who serve them.