Androgen receptor gene CAG trinucleotide repeats in anovulatory infertility and polycystic ovaries

Hyperandrogenism is currently thought to be central to the pathogenesis of polycystic ovarian syndrome (PCOS), a common endocrine disorder in premenop ausal women characterized by irregular menstruation and anovulatory inferti lity. Although hyperandrogenism is characteristic, some women with PCOS hav e normal serum androgen levels. All androgens act through the X-linked andr ogen receptor (AR), the N-terminal domain of which contains a polyglutamine tract encoded by a highly polymorphic CAG trinucleotide repeat tract. Rece ntly, variations in this CAG microsatellite tract, while remaining within t he normal polymorphic range (11-38 CAGs), have been inversely correlated wi th receptor activity. Thus, short tracts are associated with high intrinsic AR activity and increased severity and earlier age of onset of the androge n-regulated tumor prostate cancer, whereas longer CAG tracts are associated with low AR activity and oligospermic infertility. To investigate the role of the CAG repeat tract in PCOS, we measured its length in 91 patients wit h ultrasound diagnosis of polycystic ovaries, irregular menstrual cycles, a nd anovulatory infertility and compared them to 112 control subjects of pro ven fertility with regular menses. Fluorescent-labeled DNA fragments contai ning the CAG repeat tract were amplified from leucocytic DNA, and their len gths were compared with internal size markers on an automated DNA Sequencer . There were no differences in the mean CAG length between patients and con trols when both alleles were considered together or separately. Because the re is a subset of PCOS patients whose serum androgens are normal, we compar ed differences in CAG length between patients whose serum testosterone (T) levels were below the normal laboratory mean, to those that were higher. Th ere was a trend for a lower mean CAG biallelic length among anovulatory pat ients with T less than 1.73 nmol/L compared with those whose T was more tha n 1.73 nmol/L (22.47 +/- 0.36 vs. 23.25 +/- 0.29). This difference in CAG l ength between patients with low and high T levels (20.38 +/- 0.51 vs. 21.98 +/- 0.29) was highly significant (P = 0.004) when only the shorter allele of each individual was considered. Ethnic differences were also evident in our data; Indian subjects had a significantly shorter AR-CAG length compare d with Chinese, being 22.08 +/- 0.50 and 23.16 +/- 0.17, respectively. Our data indicate an association between short CAG repeat length and the subset of anovulatory patients with low serum androgens, suggesting that the path ogenic mechanism of polycystic ovaries in these patients could be due to th e increased intrinsic androgenic activity associated with short AR alleles.