2D:4D Finger Length Ratios in Individuals with Gender Dysphoria

The neurobiological basis of Gender Dysphoria (GD) is not yet fully known. In recent years, the role of prenatal exposure to testosterone has been emphasized in the development of the GD. The aim of this study was to compare the 2D:4D digit ratio, which is considered to be a morphological indicator of exposure to testosterone in the prenatal period, in individuals with GD.

The study included 99 participants diagnosed with GD comprising 54 assigned the female gender at birth [AFB-GD], 45 assigned the male gender at birth [AMB-GD], and 58 female and 58 male participants making up the control group. The right and the left hands of the participants were photocopied and finger lengths were measured using digital calipers.

The 2D:4D digit ratio on the right hand of the AFB-GD group was significantly lower (p=0.028) than that of the female controls, but it did not differ significantly as compared to male controls. The ratio on the left hand of the AFB-GD group did not significantly differ from that of the female controls, but it was higher than that of the male controls (p=0.045). The 2D:4D digit ratio on the right hand of the AMB-GD group did not differ significantly from that of the male controls, but they had a lower finger ratio as compared to the female controls (p<0.001). The ratio on the left hand of the AMB-GD group did not differ significantly from those of the male and female controls.

The results of this study present suggestive evidence that the AFB-GD individuals were exposed to testosterone in the prenatal period.