A novel homozygous nonsense variant of AK7 is associated with multiple morphological abnormalities of the sperm flagella (MMAF)

Abstract

Research Question

What novel genetic factors are associated with multiple morphological abnormalities of the sperm flagella (MMAF), a specific type of oligoasthenoteratozoospermia that leads to male infertility? However, a complete understanding of the genetic etiology of MMAF remains elusive.

Design

Whole-exome sequencing and Sanger sequencing were performed to identify potential gene variants. Immunoblotting and immunofluorescence were applied to confirm the relationship between mutated genes and disease phenotypes. ROS (reactive oxygen species) and apoptosis levels were measured to evaluate sperm mitochondrial function. Transmission electron microscopy and scanning electron microscopy were employed to observe sperm ultrastructure.

Results

A novel homozygous nonsense variant of AK7, c.1153A>T (p. Lys385*), was identified in two infertile siblings with asthenoteratozoospermia through whole-exome sequencing. Both immunoblotting and immunofluorescence assays showed a practically complete absence of AK7 in the patient's spermatozoa. Additionally, the individual with the novel AK7 variant exhibited a phenotype characterized by severe oxidative stress and apoptosis caused by mitochondrial metabolic dysfunction of spermatozoa. Notably, remarkable flagellar defects with multiple axonemes in uniflagellate spermatozoa, accompanied by mitochondrial vacuolization were observed, which has not been previously reported in patients with other AK7 variants.

Conclusions

Our experimental findings in human subjects demonstrate that a novel identified homozygous nonsense variant of AK7 may potentially be associated with MMAF-related asthenoteratozoospermia. The observed functional associations between mitochondria and sperm flagellar assembly provide evidence for potential mutual regulation between AK7 and flagella-associated proteins during spermatogenesis.