A polymorphism of the CYP17 gene related to sex steroid metabolism is associated with female-to-male but not male-to-female transsexualism

Objective

To assess the association between transsexualism and allele and genotype frequencies of the common cytochrome P450 (CYP) 17 −34 T>C single nucleotide polymorphism (SNP).

Design

Case-control study.

Setting

Academic research institution.

Patient(s)

102 male-to-female (MtF) and 49 female-to-male (FtM) transsexuals, 756 male controls, and 915 female controls.

Intervention(s)

Buccal swabs and multiplex polymerase chain reaction on a microarray system.

Main Outcome Measure(s)

Analysis of the CYP17 −34 T>C SNP.

Result(s)

CYP17 −34 T>C SNP allele frequencies were statistically significantly different between FtM transsexuals and female controls (CYP17 T: 55/98 [56%] and CYP17 C: 43/98 [44%] versus CYP17 T: 1253/1826 [69%] and CYP17 C: 573/1826 [31%], respectively). In accordance, genotype distributions were also different between FtM transsexuals and female controls using a recessive genotype model (CYP17 T/T+T/C: 39/49 [80%] and C/C 10/49 [20%] vs. CYP17 T/T+T/C: 821/913 [90%] and C/C 92/913 [10%], respectively). The CYP17 −34 T>C allele and genotype distributions were not statistically significantly different between MtF transsexuals and male controls. Of note, the CYP17 −34 T>C allele distribution was gender-specific among controls (CYP17 C: males; 604 of 1512 [40%] vs. females; 573 of 1826 [31%]). The MtF transsexuals had an allele distribution equivalent to male controls, whereas FtM transsexuals did not follow the gender-specific allele distribution of female controls but rather had an allele distribution equivalent to MtF transsexuals and male controls.

Conclusion(s)

These data support CYP17 as a candidate gene of FtM transsexualism and indicate that loss of a female-specific CYP17 T −34C allele distribution pattern is associated with FtM transsexualism.

Key Words: Transsexualism, gender, sex steroids, polymorphism, CYP17