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Androgen Receptor Gene CAG Trinucleotide Repeats in Anovulatory Infertility and Polycystic Ovaries

Departments of Obstetrics and Gynaecology (A.M., E.L.Y.) and Paediatrics (S.R.), National University of Singapore, Singapore 119074, Republic of Singapore

Address correspondence and requests for reprints to: Dr. E. L. Yong, Department Obstetrics and Gynaecology, National University Hospital, Level 2, Lower Kent Ridge Road, Singapore 119074, Republic of Singapore. E-mail: obgyel{at}nus.edu.sg

Hyperandrogenism is currently thought to be central to the pathogenesis of polycystic ovarian syndrome (PCOS), a common endocrine disorder in premenopausal women characterized by irregular menstruation and anovulatory infertility. Although hyperandrogenism is characteristic, some women with PCOS have normal serum androgen levels. All androgens act through the X-linked androgen receptor (AR), the N-terminal domain of which contains a polyglutamine tract encoded by a highly polymorphic CAG trinucleotide repeat tract. Recently, variations in this CAG microsatellite tract, while remaining within the normal polymorphic range (11–38 CAGs), have been inversely correlated with receptor activity. Thus, short tracts are associated with high intrinsic AR activity and increased severity and earlier age of onset of the androgen-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 with ultrasound diagnosis of polycystic ovaries, irregular menstrual cycles, and anovulatory infertility and compared them to 112 control subjects of proven fertility with regular menses. Fluorescent-labeled DNA fragments containing the CAG repeat tract were amplified from leucocytic DNA, and their lengths were compared with internal size markers on an automated DNA Sequencer. There were no differences in the mean CAG length between patients and controls when both alleles were considered together or separately. Because there is a subset of PCOS patients whose serum androgens are normal, we compared differences in CAG length between patients whose serum testosterone (T) levels were below the normal laboratory mean, to those that were higher. There was a trend for a lower mean CAG biallelic length among anovulatory patients with T less than 1.73 nmol/L compared with those whose T was more than 1.73 nmol/L (22.47 ± 0.36 vs. 23.25 ± 0.29). This difference in CAG length 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 compared 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 pathogenic mechanism of polycystic ovaries in these patients could be due to the increased intrinsic androgenic activity associated with short AR alleles.

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