A gain-of-function mutation in ATP6V0A4 drives primary distal renal tubular alkalosis with enhanced V-ATPase activity.

The ATP6V0A4 gene encodes the a4 subunit of Vacuolar H+-ATPase (V-ATPase), which mediates hydrogen ion transport across the membrane. Previous studies have suggested that mutations in ATP6V0A4 consistently result in a loss of function (LOF), impairing the hydrogen ion transport efficacy of V-ATPase and leading to distal renal tubular acidosis (dRTA) and sensorineural hearing loss. Here, we identified a 32-year-old male patient and his father, both of whom harbored a heterozygous ATP6V0A4 p.V512L mutation, and both exhibited with hypochloremic metabolic alkalosis, acidic urine and hypokalemia. Through a series of protein structural analyses and functional experiments, the V512L mutation was confirmed as a gain-of-function (GOF) mutation in the ATP6V0A4 gene. V512-a4 increased a4 subunit expression abundance by enhancing V512L-a4 stability and reducing its degradation, which in turn potentiated V-ATPase's capacity to acidify the tubular lumen, leading to acidic urine and metabolic alkalosis. Through mutant V512L-a4 subunit structure-based virtual and experimental screening, we discovered F351 (C25H26FN3O2S), a small-molecule inhibitor specifically targeting the V512L-a4 mutant. In conclusion, we identify a GOF mutation in the ATP6V0A4 gene, broadening its phenotypic and mutational spectrum, and provide valuable insights into potential therapeutic approaches for diseases associated with ATP6V0A4 mutations.