Mutations in the mitochondrial cytochrome B (MT-CYB) gene in spermatozoa of patients from infertile couples

Abstract

Introduction. A relevant issue of modern andrology is the identification of etiological factors of male infertility. One cause of male infertility is mitochondrial DNA (mtDNA) mutations in spermatozoa that impair their energy supply and motility. The mitochondrial genome is subject to frequent mutations and high polymorphism due to peculiarities of its structure and location, as well as its lack of recombination variability due to its mode of inheritance being strictly through the maternal line. These features are accompanied by the accumulation in spermatozoa of single-nucleotide polymorphisms in mtDNA. The aim was to identify mutations in the mitochondrial cytochrome B (MT-CYB) gene in infertile men with asthenoteratozoospermia or oligoastenoteratozoospermia. Methods. The study included 89 male patients with asthenoteratozoospermia and 65 patients with oligoastenoteratozoospermia. The comparison group consisted of 164 fertile men. The total genomic DNA, including mtDNA, was isolated with a DNA NAQIAamp Micro Kit. The genotypes of polymorphic loci in the MT-CYB gene were determined and analyzed by the TaqMan allele discrimination method. To verify mutations of the MT-CYB gene, the gene fragment was sequenced by the Sanger method on an automatic DNA analyzer, the Applied Biosystems® Sanger Sequencing 3500 Series Genetic Analyzer. Results. No single nucleotide polymorphisms rs28357373 (replacement of thymine with cytosine at position 15629) were detected in the MT-CYB gene. Therefore, this mutation is not characteristic of this patient population, and it does not contribute to the development of male infertility. Replacement of adenine with guanine at position 15218, leading to the missense mutation of p.Thr158Ala, also did not manifest itself as a cause of male infertility. Significant results were obtained by analyzing the polymorphic variant rs527236194, i.e., replacement of the CST triplet with CCC in position 15784. In patients with asthenoteratozoospermia, this mutation was much more common. Most likely, this was due to a change in gene expression with codon displacement. Conclusion. A special study is required to identify the role of the locus rs527236194 of the MT-CYB gene in the occurrence of male infertility, as well as a possibility of using it as a biomarker of the disease.