Background: Low sexual desire is present in 1/3 of male-to-female transsexuals (post-operative male-to-female transsexual persons on estrogen replacement). Several studies report lower endogenous testosterone (T) levels in this group compared to community dwelling women. However, no relationship between T and sexual desire has been found in male-to-female transsexuals. Considering its role in androgen sensitivity, cytosine-adenine-guanine (CAG) trinucleotide repeat sequence in the androgen receptor (AR) might modify the relationship between T levels and sexual desire in male-to-female transsexuals.
Aim: This study aims to assess the potential contribution of the number of CAG repeats in the association between T and sexual desire in male-to-female transsexuals. MATERIAL, SUBJECTS, AND METHODS: Thirty-four post-operative male-to-female transsexuals participated in a cross-sectional study. The Sexual Desire Inventory, a questionnaire measuring sexual desire, was completed. Serum levels of total (TT) and free T (FT), DHEA-S, SHBG, and LH were measured in morning blood samples. AR gene CAG repeat length was determined by automated DNA fragment analysis of exon 1 of the AR gene.
Results: The CAG repeat length ranged from 14 to 28 with a median of 21. CAG polymorphism was correlated with FT (r=0.389; p=0.023) but not with TT (r=0.191; p=0.280). The observed interaction between TT and CAG was significant only for solitary sexual desire (p=0.002). The interaction of CAG repeats and FT on sexual desire failed to reach significance.
Conclusions: We could not establish that CAG repeat length is a consistent modulating factor in the relationship between TT or FT and sexual desire in male-to-female transsexuals.