Association of the (TAAAA)n repeat polymorphism in the sex hormone-binding globulin (SHBG) gene with polycystic ovary syndrome and relation to SHBG serum levels.

Abstract

SHBG levels are frequently low in women with polycystic ovary syndrome (PCOS) and may contribute to increased tissue exposure to free androgens. A (TAAAA)n repeat polymorphism in the promoter of the SHBG gene has been described recently, and its transcriptional activity has been shown to be related to the number of tandem repeats. Recent evidence also suggests that prenatal exposure to androgen excess may program for the development of the PCOS phenotype during adulthood. Our aim was to investigate the possible association of the functional (TAAAA)n polymorphism in the promoter of the SHBG gene with PCOS and its relation to SHBG levels. We studied 185 women with PCOS and 324 normal controls. Genotype analysis revealed six (TAAAA)n alleles containing 6-11 repeats. The distribution of these alleles was different in the two groups. Women with PCOS had a significantly greater frequency of longer (TAAAA)n alleles (more than eight repeats) than normal women who had shorter alleles (less than eight repeats) in higher frequency (P = 0.001). Furthermore, in the PCOS group, carriers of the longer allele genotypes had lower SHBG levels [1.17 +/- 0.68 micro g/dl (35.1 +/- 20.5 nmol/liter)] than those with shorter alleles [1.51 +/- 0.93 microg/dl (45.3 +/- 28 nmol/liter P = 0.02). A novel (TAAAA)n allele, which has not been previously reported, was found in low frequency, mainly in the control population. From these results, there is evidence that there may be a genetic contribution to decreased SHBG levels frequently seen in women with PCOS. The SHBG gene may act as a susceptibility gene for PCOS and may provide the genetic link for the developmental origin hypothesis for PCOS that was recently proposed on the basis of experimental observation in prenatally androgenized sheep and primates.