The NOP2/Sun domain family, member 7 (Nsun7) gene, which encodes putative methyltransferase Nsun7, hasaroleinspermmotilityinmice.Inhumans,thisgeneislocatedonchromosome4with12exons.Theaimofthepresent studywastoinvestigatemutationsofexon7inthenormospermicandasthenospermicmen.Semensampleswerecollected fromtheFatemezahraIVFcentre(Babol,Iran)andanalysedonthebasisofWorldHealthOrganization(WHO)guidelines using general phenol–chloroform DNA extraction methods. Exon 7 was amplified using Sun7-F and Sun7-R primers. Bands on samples from asthenospermic men that exhibited different patterns of movement on single-strand conformation polymorphism gels compared with normal samples were identified and subjected to sequencing for further identification of possible mutations. Direct sequencing of polymerase chain reaction (PCR) products, along with their analysis, confirmed C26232T-transition and T26248G-transversion mutations in asthenospermic men. Comparison of normal and mutant protein structures ofNsun7indicated thattheaminoacid serine was convertedto alanine,thestructure ofthehelix, coil and strand was changed, and the protein folding and ligand binding sites were changed in samples from asthenospermic men with a transversion mutation in exon 7, indicating impairment of protein function. Because Nsun7 gene products have a role in sperm motility, if an impairment occurs in exon 7 of this gene, it may lead to infertility. The transversion mutation in exon 7 of the Nsun7 gene can be used as an infertility marker in asthenospermic men.
