ATP4A encodes the catalytic α-subunit of the gastric H+/K+-ATPase pump, a P-type ATPase located on parietal cell apical membranes 1. This enzyme uses ATP hydrolysis to generate a million-fold proton gradient, acidifying gastric juice to pH 1 by exchanging intracellular H+ ions for luminal K+ ions 1. The transport cycle involves ATP-driven phosphorylation, causing conformational shifts between inward-facing (E1) and outward-facing (E2) states 1. ATP4A expression shows age and sex dimorphism, with higher expression in men under 35 years compared to those over 50 2. Clinically, ATP4A dysfunction is relevant to multiple gastric pathologies. In gastric cancer, ATP4A expression is downregulated through intragenic DNA methylation, with methylated ATP4B detectable in patient plasma as a potential biomarker 3. ATP4A, alongside ATP4B, serves as a diagnostic biomarker for gastric cancer using machine learning models, achieving 0.99 AUC on external validation 4. In autoimmune gastritis, ATP4A is extensively downregulated, associated with marked intestinal trans-differentiation and neuroendocrine tumorigenesis risk 5. Additionally, ATP4A autoantibodies appear in pediatric type 1 diabetes patients (17% prevalence), correlating with lower vitamin B12 and ferritin levels, suggesting screening recommendations 6. Proton pump inhibitors like omeprazole and rabeprazole interact potently with ATP4A, informing therapeutic development 1.