Investigation of second to fourth finger length ratio (2D:4D) in patients with bipolar disorder

The etiology of bipolar disorder has yet to be fully elucidated, but differences in sex hormones have been suggested to play a role in its pathogenesis. An easily assessed marker of prenatal androgen exposure is the second-to-fourth-digit ratio (2D:4D) of the hand. In this study, we aimed to compare the 2D:4D ratio of patients with bipolar disorder to that of healthy controls.

Seventy patients with bipolar disorder and 70 healthy controls, matched for age and sex, were included in the study. Finger lengths were measured from the palmar digital crease to the tip using a digital vernier caliper.

Patients with bipolar disorder had considerably higher right-hand 2D:4D ratios compared to controls. Both the right and left 2D:4D ratios of male patients were significantly greater than those of males in the control group. Female patients showed no differences in right or left 2D:4D ratio compared to healthy controls.

These findings suggest that a high 2D:4D digit ratio of right hand is associated with the presence of bipolar disorder in males. Further large-scale, prospective studies are needed to explain the validity of this marker and its relationship with bipolar disorder.