title: A polymorphism of the CYP17 gene related to sex steroid metabolism is associated with female-to-male but not male-to-female transsexualism.
abstract: 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).
  
  
  METHODS
  Case-control study.
  
  
  METHODS
  Academic research institution.
  
  
  METHODS
  102 male-to-female (MtF) and 49 female-to-male (FtM) transsexuals, 756 male controls, and 915 female controls.
  
  
  METHODS
  Buccal swabs and multiplex polymerase chain reaction on a microarray system.
  
  
  METHODS
  Analysis of the CYP17 -34 T>C SNP.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Gynecologic Endocrinology and Reproductive Medicine, Medical University Vienna, Vienna, Austria.
authors.forename: Eva-Katrin
authors.initials: EK
authors.lastname: Bentz
authors.forename: Lukas A
authors.initials: LA
authors.lastname: Hefler
authors.forename: Ulrike
authors.initials: U
authors.lastname: Kaufmann
authors.forename: Johannes C
authors.initials: JC
authors.lastname: Huber
authors.forename: Andrea
authors.initials: A
authors.lastname: Kolbus
authors.forename: Clemens B
authors.initials: CB
authors.lastname: Tempfer
mesh_terms: D000328:Adult; D016022:Case-Control Studies; D005260:Female; D005787:Gene Frequency; D020022:Genetic Predisposition to Disease; D005838:Genotype; D012739:Gonadal Steroid Hormones / Q000378:metabolism*; D006801:Humans; D008297:Male; D008875:Middle Aged; D010641:Phenotype; D020641:Polymorphism, Single Nucleotide; D013254:Steroid 17-alpha-Hydroxylase / Q000235:genetics* / Q000378:metabolism; D014189:Transsexualism / Q000201:enzymology / Q000235:genetics*; D044465:White People / Q000235:genetics
chemical_list: D012739:Gonadal Steroid Hormones; D013254:Steroid 17-alpha-Hydroxylase