Association between CAG repeat number in the androgen receptor and male infertility in a Belgian study

To the Editor: The androgen receptor (AR) contains a polymorphic CAG repeat in the first exon coding for a polyglutamine (polyGln) tract (1, 2). Normal AR alleles contain between 11 and 31 repeats and are on average somewhat larger in Asians (3). Expansion of the CAG repeat to 40 or more causes an X-linked motor neuron disease called spinal and bulbar muscular atrophy (SMBA) or Kennedy’s disease (1, 2). These patients also show signs of progressive androgen resistance (progressive sexual disturbances, testicular atrophy and deterioration of sperm quality). Tut et al. (4) reported an association between long normal CAG repeats in the AR and impaired sperm production in Chinese men. In their study, 28 or more Gln in the AR was statistically more frequently observed in the group of men with infertility or subfertility compared to normal men (odds ratio=4.02 with 95% confidence interval (CI): 3.2–4.9). The opposite phenomenon was observed for ARs with 23 or less Gln. In 6itro expression experiments showed an inverse relation between the length of the Gln tract in the AR and trans-activation function (4). In a letter to the editor in this journal Lundberg Giwercman et al. (5) reported recently that, in Swedish men, no association could be found between defective spermatogenesis and AR CAG repeat length. They analysed 33 men with abnormal sperm samples and 294 controls. The observed alleles ranged from 8 to 30 CAG repeats with 21 as the most frequent allele. The repeat lengths in Swedish men were somewhat shorter on average than those observed in the Chinese men. The lack of an association was explained by possible differences in ethnic origin or by the small number of men with fertility problems in the Swedish study. To study the possible effect of different CAG repeats in the AR on male fertility in Belgian men, we genotyped 223 infertile men involved in an intracytoplasmic sperm injection (ICSI) treatment programme. We compared the results with data obtained from 181 unselected Belgian men. PCR was performed with primers flanking the CAG repeat in exon 1 of the AR gene. Three different CAG alleles were sequenced, containing 16, 24 and 43 CAG repeats. The number of CAG repeats in the other samples was calculated by comparing the size of PCR products of unknown alleles with the PCR products from individuals with a sequenced allele. The alleles observed contained between 14 and 30 CAG repeats, with 21 CAG repeats as median and most frequent class in both groups (Fig. 1). More individuals with long normal repeats were observed in the infertile group than in the controls (Fig. 1). In Asian men, the median and modus of the CAG repeat distribution in the AR is one CAG larger (22 CAG) than in Caucasian men (21 CAG) (3). Therefore, we chose 27 or more Gln as the cut-off value. Twenty-seven Gln in a population of Caucasians compares to 28 Gln in Asian men (4). There were 18 infertile individuals (8.1%) with CAG repeats of 26 or longer (=27 or more Gln, CAG’s are followed by one CAA) and only 4 (2.2%) in the control males. This results in an OR of 3.09 (x=5.25; p=0.022, 95% CI: 1.06–10.63). Subdividing the infertile males according to sperm counts does not result in a trend of increased frequency of longer alleles in the groups with fewer sperm counts (Table 1), as was observed in the Chinese study (4). Our data show the same range of CAG alleles as in the Swedish study and a smaller mean CAG repeat length than in the Chinese study. In our study we could confirm, however, that more males with spermatogenesis problems had longer normal CAG repeats than expected for the control population of Belgian males. The absence of a similar association in the Swedish study might be due to a lack of power (only 33 infertile males included). A long normal CAG repeat is probably only an important factor if other factors are also present