GALNTL5 is a testis-specific glycosyltransferase-like protein essential for male reproductive function. Primary function: GALNTL5 localizes to the sperm neck region and acrosome during spermatid development, where it binds N-acetylgalactosamine (GalNAc) 1. Mechanism: The protein is required for proper acrosomal protein loading and ubiquitin-proteasome system localization 2. GALNTL5 mediates sperm binding to the zona pellucida and uterotubal junction through GalNAc interactions, enabling sperm migration and fertilization 1. Disease relevance: GALNTL5 mutations cause asthenozoospermia (reduced sperm motility) and male infertility by impairing glycolytic enzyme abundance and sperm motility 23. Heterozygous and homozygous mutations both reduce fertility significantly 4. Additionally, genomic deletions in GALNTL5 associate with increased risk of arsenic-induced skin lesions 5, and the gene shows altered expression in kidney disease and certain cancers, though its role in these contexts remains unclear 67. Clinical significance: GALNTL5 genetic screening and targeted sperm selection enable reproductive success in affected patients via intracytoplasmic sperm injection 3.