A novel frameshift variant in TTC29 associated with total asthenozoospermia and male infertility

Severe sperm motility defects are an important cause of male infertility and are frequently associated with sperm flagellar abnormalities. TTC29 encodes an evolutionarily conserved axonemal protein implicated in sperm flagellar assembly and motility, yet the pathogenic mechanisms of TTC29 variants remain incompletely understood.

A Chinese man with total asthenozoospermia was investigated using whole-exome sequencing, Sanger sequencing, transmission electron microscopy, sperm immunofluorescence, and heterologous expression analysis in HEK293 T cells. The clinical outcome following intracytoplasmic sperm injection (ICSI) was also evaluated.

Whole-exome sequencing identified a novel TTC29 frameshift variant (NM_031956.4:c.121dupA; p. Ile41Asnfs*21), which was confirmed by Sanger sequencing. Transmission electron microscopy revealed severe ultrastructural abnormalities involving both the midpiece and principal piece, with disruption of the canonical 9 + 2 axonemal architecture and marked abnormalities of peri-axonemal structures. In representative immunofluorescence images, TTC29 signal was readily detected along the sperm flagellum in the fertile control, whereas a visibly weaker signal was observed in spermatozoa from the proband. Heterologous expression analysis showed little or no detectable production of the expected TTC29 protein product from the mutant construct. Although fertilization was achieved following two ICSI cycles, no clinical pregnancy was obtained.

We identified a novel TTC29 frameshift variant associated with total asthenozoospermia and male infertility. Genetic, ultrastructural, and heterologous expression evidence supports a deleterious effect of the identified TTC29 variant, thereby expanding the mutational spectrum of TTC29-related infertility and providing further insight into the molecular basis of severe sperm motility disorders.