# Distinct Second-to-Fourth Digit Ratio Among Patients With Schizophrenia

## TL;DR

This study found that people with schizophrenia have different finger length ratios compared to healthy individuals, suggesting prenatal hormone differences may contribute to the condition.

## Contribution

The study demonstrates that sexual dimorphism in 2D:4D ratios is absent in schizophrenia patients, linking prenatal hormone exposure to the disorder's origins.

## Key findings

- Healthy women had higher 2D:4D ratios than men, showing sexual dimorphism.
- Schizophrenia patients showed less sexual dimorphism in 2D:4D ratios.
- Female patients displayed more masculine digit ratios compared to healthy women.

## Abstract

Background: It has been suggested that prenatal sex hormones may have a substantial impact on brain development and mental illness. The second-to-fourth digit (2D:4D) ratio, a critical retrospective marker for the secretion of prenatal sex hormones, can be measured and compared between healthy people and patients with schizophrenia as a direct way to support the hypothesis.

Aim: This study aimed to examine whether sexual dimorphism is held in a 2D:4D ratio and further test the hypothesis that patients with schizophrenia have distinct 2D:4D ratios from healthy people.

Setting: The study was conducted at a local hospital in a typical mid-size city in the eastern part of China.

Methods: The study was performed by analyzing the 2D:4D ratios in both hands from the control group and patient group, respectively, with the application of statistical measurements (means, variances, and correlations), the independent-sample t-test, and the paired-samples t-test. In terms of the sample size, a total of 108 healthy participants were included in our study, comprising 33 men and 75 women, with a mean age of 30.55 years. Besides, there were 126 individuals with schizophrenia in the study, comprising 73 men and 53 women, with an average age of 44.2 years.

Results: The results showed that the 2D:4D ratio of women in the control group (mean value of the left hand: 0.9650; mean value of the right hand: 0.9562) was significantly higher than that of men (mean value of the left hand: 0.9418; mean value of the right hand: 0.9298), indicating that the sexual dimorphism is held in the 2D:4D ratio (left hand p-value: 0.003<0.05; right hand p-value: 0.004<0.05). This effect, however, was not observed in the patient group. Instead, the female patients displayed more masculine digit ratios, whereas the male patients' hands displayed fewer masculine patterns.

Conclusion: The results provide evidence that the pathogenesis of schizophrenia is related to abnormal prenatal sex hormone secretion. The research on the 2D:4D ratio as a biomarker should be able to help contribute to the literature on the pathogenesis of schizophrenia.