Androgen receptor gene CAG and GGN polymorphisms in infertile Nigerian men

The human androgen receptor gene (AR) is an important regulator of male sexual development including spermatogenesis. Exon 1 of this gene encodes the N terminal domain, which controls transcriptional activity of the receptor and the two polymorphic repeats CAG and GGN. Many studies have reported association of the expanded CAG repeat length with male infertility, although this is still controversial. The GGN repeat, in contrast, has been less thoroughly studied. Thus far, only scanty studies have been reported from African populations and none from Nigeria. Therefore, we have investigated the possible association between AR polymorphism repeats length (CAG and GGN) and reduced spermatogenesis in infertile Nigerian men (no.=60) consisting of 20 non-obstructive azoospermic and 40 oligozoospermic subjects compared with controls with normozoospermia and proven evidence of fertility (no.=38). In addition, 48 volunteers with normal spermatogenesis were recruited from a German population. CAG and GGN repeats length were determined by fragment length analysis using GeneScan. The CAG and GGN repeats length of infertile compared to fertile populations were not significantly different (p>0.05). We found a unique AR GGN allele distribution with 20-23 GGN repeats predominant in the Nigerian study population. Our results show that CAG and GGN repeats polymorphisms are not a critical index of male infertility. While we do not find a relationship with CAG and GGN repeats haplotypes and male infertility, we report for the first time a unique and wider distribution of the GGN allele in the Nigerian population which is significantly different from the Caucasian population. The functional relevance of this variance to male fertility warrants in-depth elucidation.