AHCYL2 (adenosylhomocysteinase like 2) is a cytosolic protein involved in ion transport regulation and metabolic homeostasis. Primary function: AHCYL2 acts as a regulatory protein for the electrogenic sodium/bicarbonate cotransporter NBCe1-B (SLC4A4), modulating its sensitivity to intracellular magnesium 1. Unlike its homolog AHCYL1, AHCYL2 does not regulate inositol 1,4,5-trisphosphate receptor sensitivity 2. The protein participates in adenosylhomocysteinase activity and the L-methionine cycle 2. Mechanism: AHCYL2 interacts directly with NBCe1-B to reduce apparent magnesium affinity for channel inhibition specifically under bicarbonate-deficient conditions 1. Disease relevance: AHCYL2 dysregulation is implicated in multiple pathologies. In recurrent implantation failure, miR-665-mediated downregulation of AHCYL2 disrupts endometrial angiogenesis and cell adhesion 3. AHCYL2 expression is reduced in colorectal cancer tissues compared to healthy mucosa 4. Variants are associated with conotruncal heart defect susceptibility through maternal-fetal genotype interactions 5. AHCYL2 appears as a hub gene in schizophrenia immune dysfunction 6 and stomach adenocarcinoma prognostic models 7. Long-term nitrogen oxide exposure alters AHCYL2 expression and methylation in peripheral blood 8. Clinical significance: AHCYL2 emerges as a potential biomarker for reproductive dysfunction, gastrointestinal cancers, and psychiatric disorders, though mechanistic understanding remains incomplete.