Association Study Between Single Nucleotide Polymorphism Of DNMT1、KIT And KITLG Gene With Dyszoospermia

Male infertility is a polygenic disease caused by a genetic, environment, food and many other factors. In recent years, infertility has been becoming one of the most common diseases in the world. In the general population, there are about10-15%of couples can not normally reproduce offspring and half of these couples are due to male infertility. It is estimated that there are approximately4%to5%of men with male infertility caused by genetic factors. Spermatogenesis disorder is one of the most common reasons leading to the male infertility, and genetic factors play an important role in impaired spermatogenesis. In recent years, the studies on the pathogenesis of impaired spermatogenesis have made some progress and found several genetic factors associated with impaired spermatogenesis, such as chromosome abnormalities, lack of the Y chromosome and some gene mutation and so on. However, these known factors just can explain a part of this disease; there still are many genetic causes of impaired spermatogenesis need to be further clarified. Spermatogenesis is a complex process, including spermatagonial cells proliferation and differentiation, meiosis and differentiation of sperm, in which numerous genes are involved. Thus, these genes playing role in spermatogenesis are considered an important candidate impaired spermatogenesis. It will provide valuable information for the elucidation on the genetic causes of male infertility and pathogenesis to study the relationship of candidate genes and impaired spermatogenesis.DNMT1(DNAmethyltransferasel) gene is an important candidate gene for impaired spermatogenesis. It encodes DNMT1which is a DNA methyltransferase playing a role in the methylation of DNA. The researches showed that the expression and regulation of many genes are involved in spermatogenesis, and DNA methylation of certain genes is essential for normal spermatogenesis. DNMT1is expressed in all stages of human spermatogenesis including proliferation, meiosis, spermatids differentiation and in ejaculated spermatozoa, which indicates the importance of DNMT1for spermatogenesis. Studies have shown that the abnormal expression of DNMT1gene can lead to apoptosis of germ cells and impaired spermatogenesis in mice. In humans, abnormal DNMT1expression was also observed in testis of patients with impaired spermatogenesis. These data suggested that DNMT1is crucial for spermatogenesis and may play a role inspermatogenesis impairment and male infertility.In recent years, the roles of some signal transduction systems in impaired spermatogenesis are paid more attentions. KIT/KITLG system is an important signal system in regulation of normal development of germ cells. The product of KIT gene is the KIT receptor that is a tyrosine kinase receptor (tyrosine kinase receptor). The product of KITLG (KIT ligand) is KITLG which is the specific ligand of KIT. The signal system is activated by the binding of KIT and KITLG.. Numerous studies in animal models have revealed that the activation of KIT/KITLG signaling system was crucial for the proliferation, meiosis, migration, survival and maturation of the germ cells in testis. It has been demonstrated that KIT/KITLG signaling system plays an important role in spermatogenesis. In different animal models, deletions or mutations of KIT or KITLG gene could result in spermatogenesis impairment and male infertility, suggesting that the genetic variations of KIT and KITLG genes may also play a role in human spermatogenesis impairment and male infertility.Until now, there is lack of the data on the effects of variations of DNMT1gene, KIT gene and KITLG gene on human impaired spermatogenesis. In view of this,, the allele and genotype frequency distributions of six SNP locus in the three gene (rsl6999593, rs2228612and rs2228611locus of DNMT1; rs3819392locus of KIT;rs995030and rs4474514locus of KITLG) were investigated in idiopathic infertile men and fertile men using polymerase chain reaction, restriction fragment length polymorphism and DNA sequencing assays in order to explore the possible relationship between the variation of three genes and impaired spermatogenesis.This study indicated that there were significant differences in allele and genotype frequency of rs16999593, rs2228612locus in DNMT1gene between oligospermia patients and controls. The frequencies of rsl6999593allele A(83.6%versus77.6%, P=0.033) and genotype AA (69.2%versus59.0%, P=0.037) and SNP rs2228611genotype AA (18.4%versus9.9%,P=0.016) in patients with oligospermia were significantly higher than those in controls, which suggested that allele A and genotype AA of SNP rs16999593, genetype AA of rs2228611might be associated oligospermia and the polymorphism in DNMT1gene might modify the susceptibility to oligospermia.The results of study on allele and genotype frequency distributions of SNP rs3819392in KIT gene as well as rs995030and rs4474514in KITLG gene revealed that allele and genotype frequencies of rs3819392in KIT gene and rs4474514in KITLG gene were significant different between the patients with oligospermia and controls. The frequencies of allele G (94.2%versus90.0%p=0.022) and genotype GG (89.2%versus82.0%p=0.042) in patients with oligospermia were significantly higher than those in controls at rs3819392locus in KIT gene. In addition, the genotype CC of rs4474514in KITLG (8.2%versus3.4%, p=0.034) also significantly increased in oligospermic patients in comparison to controls. These findings indicated that SNP rs3819392in KIT gene and rs4474514in KITLG gene may be associated with oligospermia.