A novel NPHP4 homozygous missense variant identified in infertile brothers with multiple morphological abnormalities of the sperm flagella.

Abstract

Asthenozoospermia is an important cause of male infertility, and the most serious type is characterized by multiple morphological abnormalities of the sperm flagella (MMAF). However, the precise etiology of MMAF remains unknown. In the current study, we recruited a consanguineous Pakistani family with two infertile brothers suffering from primary infertility due to MMAF without obvious signs of PCD. We performed whole-exome sequencing on DNAs of the patients, their parents, and a fertile brother and identified the homozygous missense variant (c.1490C > G (p.P497R) in NPHP4 as the candidate mutation for male infertility in this family. Sanger sequencing confirmed that this mutation recessively co-segregated with the MMAF in this family. In silico analysis revealed that the mutation site is conserved across different species, and the identified mutation also causes abnormalities in the structure and hydrophobic interactions of the NPHP4 protein. Different bioinformatics tools predict that NPHP4p.P497R mutation is pathogenic. Furthermore, Papanicolaou staining and scanning electron microscopy of sperm revealed that affected individuals displayed typical MMAF phenotype with a high percentage of coiled, bent, short, absent, and/or irregular flagella. Transmission electron microscopy images of the patient's spermatozoa revealed significant anomalies in the sperm flagella with the absence of a central pair of microtubules (9 + 0) in every section scored. Taken together, these results show that the homozygous missense mutation in NPHP4 is associated with MMAF.