To investigate the genetic cause of male infertility characterized by severe asthenozoospermia, two unrelated infertile men with severe asthenozoospermia from nonconsanguineous Chinese families were enrolled, and whole exome sequencing were performed to identify the potential pathogenic mutations. Novel compound heterozygous mutations (NK062 III-1: c.290T>C, p.Leu97Pro; c.1664delT, p.Ile555Thrfs*11/NK038 III-1: c.212G>T, p.Arg71Leu; c.290T>C, p.Leu97Pro) in SLC26A8 were identified. All mutations were inherited from their heterozygous parents and are predicted to be disease-causing by SIFT, PolyPhen-2, Mutation Taster and CADD. In silico mutant SLC26A8 models predict that mutations p.Leu97Pro and p.Arg71Leu cause changes in the α-helix, which may result in functional defects in the protein. Notably, heterozygous male carriers of each mutation in both families were able to reproduce naturally, which is inconsistent with previous reports. Ultrastructural analysis revealed severe asthenozoospermia associated with absence of the mitochondrial sheath and annulus in spermatozoa from both the probands, and both structural defects were verified by HSP60 and SEPT4 immunofluorescence analysis. SLC26A8 levels were significantly reduced in spermatozoa from patients harboring biallelic SLC26A8 mutations, and both patients achieved good prognosis following intracytoplasmic sperm injection. Our findings indicate that mutations in SLC26A8 could manifest as a recessive genetic cause of severe asthenozoospermia and male infertility.

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