The Ratio of Second and Fourth Digit Length: A Biomarker for Methamphetamine Dependence?

The ratio of 2nd and 4th digit length (2D:4D) is considered to be a sexually dimorphic trait. Low 2D:4D is implicated in alcohol dependence and heroin dependence and correlated with psychological traits such as aggression, physical aggression, and sensation. The purpose of this study is to compare the 2D:4D between methamphetamine (METH) dependence and controls and the 2D:4D ratio that is a potential biomarker for METH dependence.

In this study, 40 patients diagnosed with METH dependence in Eulji University Gangnam Eulji Hospital and 50 healthy volunteers were all employees in the same hospital. Images of participants' hands were created using a scanning device. The images contained both the right and left hands; computer software was used to measure the 2D:4D ratio for both hands. We compared the ratios, analyzed by t test, between the METH dependence group and the control group.

The mean 2D:4D values were 0.941 (right hand) and 0.943 (left hand) for the patients with METH dependence; in contrast, they were 0.961 (right hand) and 0.961 (left hand) for the control group. These values were significantly smaller than the control in patients' right hands (p = 0.003) and left hands (p = 0.012).

Patients with METH dependence had smaller 2D:4D ratios than those in the control group, which is similar to the results from the previous substance use disorder studies. Thus, elevated prenatal testosterone levels during the gonadal period could be related to future METH problems. Furthermore, the 2D:4D ratio is a potential marker for the prediction of METH dependence.