DEFB126 encodes an atypical beta-defensin that plays critical roles in sperm function and male fertility. This highly glycosylated protein consists of a conserved beta-defensin core and a unique long glycosylated peptide tail that becomes adsorbed onto the entire sperm surface during epididymal maturation 1. DEFB126 facilitates sperm transport through cervical mucus via its high negative charge, which appears critical for sperm penetration 2. The protein protects sperm from immune recognition in the female reproductive tract, with the sialic acid moieties providing immune cloaking properties 3. DEFB126 is positively correlated with sperm motility and morphology, with higher proportions found in motile sperm 4. A common 2-nucleotide deletion in the DEFB126 gene results in a null allele associated with male subfertility and altered sperm glycocalyx 15. Men homozygous for this deletion show reduced clinical pregnancy rates following intrauterine insemination but not IVF/ICSI 5. Additionally, the beta-defensin core exhibits antimicrobial activity and can inhibit LPS-mediated inflammation by downregulating pro-inflammatory cytokines and blocking MAPK signaling pathways 6. These findings establish DEFB126 as a multifunctional protein essential for male reproductive success.