Gender identity refers to one’s psychological experience of their own gender. For some individuals, an incongruence can occur between their gender and biological sex, which can result in significant psychological distress and be diagnosed as gender incongruence. Endocrinological, neuroanatomical, and genetic evidence suggests that a person’s gender identity can be influenced by biological factors. To explore a potential genetic basis of gender incongruence, a meta-analysis of published candidate gene association studies in transgender cohorts was conducted. Both transgender female and transgender males were considered. Genes analysed included androgen receptor, estrogen receptor alpha and beta, and CYP17, which play roles in the sex-hormone
signalling pathway. Long forms of the CAG repeat length polymorphism in the Androgen Receptor were overrepresented in the transgender male cohort (n = 1186). Short forms of this variant were also found to be overrepresented in the transgender female cohort given a homozygous genotype of the long form of the CA RFLP in Estrogen Receptor Beta. These results suggest that sex-hormone signalling may play a role in the establishment of gender identity.