CAG repeat polymorphism in androgen receptor and infertility: A case-control study

Abstract

Background: Androgens play a role in the development of male phenotype and spermatogenesis during puberty, the function of which is regulated by the androgen receptor (AR) gene. There is a polymorphism site in exon 1 of the gene encoding this receptor that can have different frequencies of CAG trinucleotide repeats and leads to the formation of polyglutamine chains of different lengths in the N-terminal domain of the AR protein and reduced sperm production by affecting spermatogenesis.
 Objective: To investigate whether the cause of a group of unexplained infertilities could be the increased frequency of CAG repeats in the AR gene of patients with oligozoospermia and azoospermia.
 Materials and Methods: In this case-control study, 84 men including 42 with unexplained infertility As a case group and 42 fertile men as a control group were selected. The frequency of CAG repeats was determined by the polymerase chain reaction method and then the difference in the frequency of these repeats was determined based on the difference in band size on the agarose gel.
 Results: The mean CAG repeat length in the azoospermia and oligozoospermia group was 17.5 ± 0.63 and in the fertile group it was 16.11 ± 0.75 (p = 0.46). In addition, most men (88.1% in the case group and 71.41% in the control group) had 13-23 repeats.
 Conclusion: No significant correlation was found between CAG repeat length and the risk of male factor infertility in an ethnically defined population of Iranian men. The role of regulatory factors and epigenetic changes should be taken into account too.
 Key words: Infertility, Azoospermia, Androgens, X chromosome, Spermatogenesis.

CAG Expansion in Androgen Receptor Gene of Infertile Men in Erbil Governorate

“…In the infertile men, the CAG expansion range is longer than the fertile men which are between (17)(18)(19)(20)(21)(22)(23)(24)(25)(26) and (21)(22)(23)(24) respectively. The current study agrees with a study done on an Iranian population [11],which showed that men with abnormal spermatogenesis had considerably in their AR gene, there are more CAG repeats than men in fertile men. Also, in another study [16], the result indicated that male infertility is correlated with a greater CAG repeat length.…”

“…The eighth exon of this gene code for an intracellular transcription factor that is a member of the nuclear receptor superfamily for steroids, this gene which produces polyglutamine has polymorphisms that may be examined including anExon 1 of the N-terminal domain contains a repetition of the CAG trinucleotide. Polyglutamine strands are produced by CAG repeats and are incorporated into the structure of the protein that is being produced [11]. Directly controlling gene transcription is the main mechanism of action for AR,after an androgen binds to its receptor, a conformational change takes place that results translocations into the nucleus, dimerization, and the dissociation of heat shock proteins, the AR dimer attaches to a region of DNA described as a component of the hormonal response, up-or down-regulating the transcription of a certain gene, additionally, AR could possibly function through a non-genomic mechanism that involves the immediate activation of kinase-signaling cascades and the regulation of intracellular levels of calcium [12].…”