CATSPER4 encodes a pore-forming subunit of the CatSper (cation channel sperm-associated) complex, a sperm-specific voltage-gated calcium channel 1. The protein contains a single channel-forming domain with a conserved pore-loop sequence (TxDxW) and coiled-coil protein-protein interaction domains in its C-terminal tail, enabling assembly into a functional hetero-tetrameric channel with CATSPER1-3 1. CATSPER4 is primarily expressed in testis and ejaculated sperm 2, with expression increasing substantially from puberty onward during spermatogenesis 2. The channel mediates calcium-dependent physiological responses essential for fertilization, including sperm hyperactivation, acrosome reaction, and oocyte chemotaxis 3. CATSPER4 demonstrates particular involvement in sperm flagellum function 4. Clinically, CATSPER4 mutations have been identified in patients with asthenozoospermia (reduced sperm motility) 5, and the gene is imprinted, suggesting heterozygous mutations may impair function 5. CATSPER4 has been identified as a hub gene and potential biomarker for nonobstructive azoospermia diagnosis 6. A genome-wide association study identified a CATSPER4 locus associated with human adult height 7, though the biological relevance of this association remains unexplored.