Objective: To investigate the digit ratio of men who have sex with men (MSM), and the relationship between digit ratio and the partner types of MSM.
Methods: Participants were required from Yunnan Rainbow Sky, a community organization that specialized in HIV testing, intervention and counseling services for MSM between December 2014 and April 2015. Inclusion criteria of MSM as the following: more than 18 years old; men who have had sex with men; HIV test was negative. Exclusion criteria were as this: those who couldn't attend the research due to disability. Eventually, there were 115 MSM participated in the research. According to the nationality, we adopted 1:1 matched case-control study, and we selected 115 men as control group. According to the partner number of MSM, the MSM were divided into two groups. One group was fixed partner and another was multi-partner. We used a questionnaire to collect the demographic characteristics, knowledge about HIV/AIDS, sexual behaviors during nearly 6 months, sexual orientation, the places where looked for sex partners, sex roles, drug use, preventive services etc. Then, the physical measurements were used to measure the length from second to the fifth finger in MSM group and control group. The results were expressed as nD. The chi-square test was used to compare the demographic differences between MSM group and the control group, and the T-test was used to compare the digit ratio between two groups.
Results: Among 115 MSM, there were 26% (30/115) MSM who had a fixed partner, and there were 74% (85/115) MSM who had multi-partner. The mean values of digit ratio of MSM presented a trend as 2D:3D < 2D:4D < 3D:4D < 2D:5D < 4D:5D < 3D:5D. The right 2D:4D and 2D:5D of MSM were 0.957 7 ± 0.048 1 and 1.229 8 ± 0.083 4, and the mean value was significasntly higher than control group (0.941 4 ± 0.038 0 and 1.204 1 ± 0.069 5, t values were 2.84, 2.54 and P values were 0.005, 0.012). The right 2D:4D of the fixed partner group and multi-partner group among MSM were 0.962 2 ± 0.051 0 and 0.956 1 ± 0.047 3, respectively, and the mean values were significantly higher than control group (t values were 2.98, 2.83; P values were 0.027, 0.015).
Conclusion: The proportion of multi-partner MSM was higher, so MSM at a high risk of being HIV infected. Right 2D:4D could be used as a biomarker of the MSM in Kunming, but couldn't reflect the features of MSM whether he has a fixed partner or has several partners.