SLC9B1 encodes NHA1 (NHEDC1), a sperm-specific Na+/H+ exchanger that plays essential roles in male fertility 1. The protein is predominantly expressed in testis, specifically localizing to seminiferous tubule cells, and functions in intracellular pH regulation of spermatozoa 2. SLC9B1 is crucial for sperm motility and fertility through its sodium-proton antiporter activity 1. The gene's expression is regulated by complex mechanisms involving DNA methylation at multiple regulatory elements, including two promoters (P1 and P2) and CpG islands, with tissue-specific methylation patterns controlling testis-specific expression 2. Interestingly, SLC9B1 methylation patterns in maternal blood samples can predict fetal intolerance of labor, with high predictive values (positive predictive values 0.80-0.89, negative predictive values 0.91-0.92), suggesting potential clinical utility in obstetric care 3. Beyond reproductive function, genome-wide association studies have identified SLC9B1 as potentially involved in diverse conditions including dilated cardiomyopathy risk and migraine susceptibility, indicating broader physiological roles 45. The protein belongs to the SLC9B subfamily of Na+/H+ exchangers, which share greater similarity to prokaryotic NHEs compared to other mammalian NHE isoforms 1.