Genetic analysis of male infertility

Approximately one in twenty men has impaired spermatogenesis due to mutation of genes involved in the establishment or maintenance of fertility. Our understanding of male infertility is complicated by the variable phenotypes produced by similar genetic changes, largely due to the practise of screening a single fertility gene in isolation. This thesis aimed to increase our understanding of the role of synergistic mutations in relation to differences in semen quality. Each sample was analysed for mutation in: CAG trinucleotide repeat variation in the X-linked androgen receptor (AR) gene, micro deletion within the three Y chromosome azoospermic factor (AZF) regions, and CAG trinucleotide repeat variation and exonuclease domain mutation in the nuclear polymerase gamma (POLγ gene. These genes have been associated with reduced semen quality in past research. Each gene region was amplified by polymerase chain reaction (PCR), followed by sequencing. Suspected AZF micro-deletions were confirmed by Southern blot hybridisation. Associations with semen quality were evaluated using either a t-test or Gtest for independence at α=0.05. Yq AZF micro-deletions were observed in 6.6% (14/211) of men with poor semen quality but not in normozoospermic samples (0/104); P<0.001). Micro-deletion frequency was greatest in azoospermic and severely oligoasthenozoospermic individuals (15% and 11.5%, respectively). AR CAG repeat length ranged from 9-38 CAG repeats in the normozoospermic population (n=98) and 13-31 CAG repeats in men with poor semen quality (n= 119). Variation in AR CAG trinucleotide repeat number was not significantly related to poor semen quality (P>0.05). Variation in POLγ CAG repeat number was not significantly different between normozoospermic men (n=93) and men with poor semen quality (n= 182); P>0.05. No nucleotide changes were observed in any of the three POLγ exonuclease motifs (n=83 normozoospermic and 191 non-normozoospermic motif, 61 and 65 motif II, and 60 and 64 motif III). Although most gene regions did not show an association with poor semen quality on their own, there was a general trend towards greater severity of impaired spermatogenesis with the presence of both Yq micro-deletion and mitochondrial DNA substitutions or moderately expanded AR CAG repeats. These results support the idea that male infertility is a complex process, due to many factors, some of which act dominantly and others act in concert

The association between Mitochondrial NADH Dehydrogenase (MTND3, MTND4L, MTND4) polymorphisms and male infertility

Male infertility has been related to many factors and about 15 - 30% of the cases are related to genetic predisposition. The purpose of the present study was to determine the relationship between infertility and the polymorphism of mitochondrial NADH dehydrogenase subunit 3, 4L, and 4 (MT-ND3, MT-ND4L, and MT-ND4) genes. Direct sequencing of the target genes in the mitochondrial DNA was carried out on semen samples of 68 subfertile and 44 fertile men. Forty single nucleotide polymorphisms in the MT-ND3, MT-ND4L, and MT-ND4 genes were identified and genotyped as follows: eight SNPs in MTND3 rs2853826, rs28435660, rs193302927, rs28358278, rs41467651, rs3899188, rs28358277 and rs28673954, seven SNPs in MTND4L rs28358280, rs28358281, rs28358279, rs2853487, rs2853488, rs193302933 and rs28532881, and twenty five SNPs in MTND4 in the cases and controls: rs2853495, rs2857284, rs2853496, rs2853497, rs3087901, rs2853493, rs2853490, rs3088053, rs2853491, rs2857285, rs28358282, rs28594904, rs28669780, rs28415973, rs28471078, rs55714831, rs28358283, rs75214962, rs28529320, rs2853494, rs28609979, rs28358286, rs28359168, rs28384199, and rs869096886. The genotypes frequencies of the study population showed that rs2853495 G>A (Gly320Gly) in the MT-ND4 gene was statistically associated with male infertility (P = 0.0351). In the allele frequency test, the results showed that rs2853495 G>A (Gly320Gly) and rs869096886 A>G (Leu164Leu) in MT-ND4 were significantly associated with male infertility (adjusted OR = 2.616, 95% CI = 1.374 - 4.983, P = 0.0028; adjusted OR = 2.237, 95% CI = 1.245 - 4.017, P = 0.0073, respectively). On the other hand, no statistically significant association difference was reported between the asthenozoospermia, oligozoospermia, teratozoospermia, asthenoteratozoospermia, oligoasthenoteratozoospermia, oligoteratozoospermia subgroups of subfertile males and the fertile ones. In conclusion, our findings suggested that male infertility was correlated to rs2853495 and rs869096886 SNPs in the MTND4 gene. More studies on the subfertile males in different populations are required to develop a clear understanding of the role of these SNPs in male infertility. In addition, functional studies will be very helpful to elucidate the molecular role of these SNPs in the function of these genes