A common polymorphism of the SRD5A2 gene and transsexualism.

The relation between genetic variation of the androgen metabolism and transsexualism is unknown. In a case-control study of 100 male-to-female (MtF) transsexuals, 47 female-to-male (FtM) transsexuals, and 1670 controls, the authors assess allele and genotype frequencies of the steroid 5-alpha reductase (SRD5A2) Val89Leu polymorphism using polymerase chain reaction. Allele and genotype frequencies are not significantly different between MtF transsexuals and male controls (SRD5A2 V: 137/200 [69%] and SRD5A2 L: 63/200 [31%] vs 1065/1510 [71%] and 445/1510 [29%], respectively; P = .6; odds ratio [OR], 1.10; 95% confidence interval [CI], 0.76-1.58; SRD5A2 V/V+V/L: 92/100 [92%] and L/L 8/100 [8%] vs SRD5A2 683/755 [91%] and 72/755 [9%], respectively, P = .7; OR, 0.82; 95% CI, 0.24-2.84). Allele and genotype frequencies are also not significantly different between FtM transsexuals and female controls (SRD5A2 V: 70/94 [74%] and SRD5A2 L: 24/94 [26%] vs 1253/1830 [69%] and 573/1830 [31%], respectively; P = .3; OR, 0.75; 95% CI, 0.45-1.26; SRD5A2 V/V+V/L: 44/47 [93%] and L/L 3/47 [7%] vs 823/915 [90%] and 92/915 [10%], respectively, P = .6; OR, 0.61; 95% CI, 0.11-3.32). Of note, there is no gender-specific genotype distribution among controls. The SRD5A2 Val89Leu SNP is not associated with transsexualism, refuting SRD5A2 as a candidate gene of transsexualism.