Male mice with a gene called Ncoa5 missing only one copy have trouble making healthy sperm, leading to infertility. The sperm from these mice have shape and movement problems in the epididymis, a part of the male reproductive system. The levels of a protein called IL-6 are higher in the epididymis of these mice, which may be causing the sperm issues. Deleting another gene called Il-6 in these mice helps improve sperm movement and fertility. This study shows that Ncoa5 plays a role in sperm development in the epididymis and that its deficiency can lead to male infertility by increasing IL-6 levels.