Required for male fertility through its role in axonemal doublet stabilization which is essential for sperm motility and fertilization. Expressed exclusively in testis. Expression starts at postnatal day 20 and continues throughout adulthood. Male subfertility. Sperm show an impaired ability to penetrate the zona pellucida and abnormal motility characterized by frequent stalling in the anti-hook position with the flagellum and hook of the sperm head pointing in opposite directions. Sperm flagella lack outer microtubule doublet 4 in 63% of mutants while doublet 7 is missing in 14.8% of mutants. A small number of mutants have multiple doublets missing but these are relatively rare: the 4th and 7th doublets are missing in 1.6% of mutants; the 4th, 5th and 7th doublets are missing in 3.7%; the 4th, 5th and 6th doublets are missing in 1.23%; and the 4th, 5th, 6th and 7th doublets are missing in 1.23%. Belongs to the CFAP97 family.