ZMYND12 is an axonemal protein essential for sperm flagellum function and male fertility. The protein localizes to the sperm axoneme where it forms a complex with TTC29 and DNAH1, components of the inner dynein arm (IDA) 1. This complex is critical for proper flagellar assembly and the coordinated bending movements required for sperm motility 2. Mechanistically, ZMYND12 functions as an IDAd subunit that maintains PRKACA protein levels in sperm, with reduced PRKACA observed in Zmynd12 knockout mice 2. ZMYND12 is also involved in sperm capacitation, a maturation process necessary for fertilization 2. Biallelic ZMYND12 variants cause asthenoteratozoospermia (reduced sperm motility with morphological abnormalities) and primary male infertility 1. Four unrelated infertile men carrying homozygous ZMYND12 variants showed altered axonemal localization of dynein arm proteins and severe flagellar defects 1. In functional models using Trypanosoma brucei and knockout mice, ZMYND12 deficiency dramatically impairs flagellar motility and reduces fertility 12. These findings establish ZMYND12 as a novel asthenoteratozoospermia-associated gene with clear clinical relevance for diagnosing genetic male infertility.