As several lines of evidence suggest that the annulus is involved in guiding flagellum assembly (in particular, in midpiece arrangement during sperm terminal differentiation), annulus defects may be be the cause of asthenozoospermia due to abnormal flagellum biogenesis in humans, a phenotype, which would be however distinct from that of Septin4 and Slc26a8 invalidation in mice. This evidence concerns the gene SLC26A8 and Reduced sperm motility.