Mutations in ammonia transporter RhBG that impair NH ₃ /NH ₄ ⁺ transport in patients with chronic kidney disease

Chronic kidney disease (CKD) imposes a substantial health burden globally, with emerging evidence pointing to the significance of metabolic acidosis and low urinary NH₄ ⁺ excretion resulting in poor CKD outcomes. The present study aims to identify in CKD patients, loss of function mutations in RhBG, one of the NH₃/NH₄ ⁺ transporters in the collecting duct, and to show that NH₃/NH₄ ⁺ transport is impaired by these mutations. Single nucleotide polymorphisms of RhBG associated with CKD occurrence were identified using ancestry-stratified data from the Chronic Renal Insufficiency Cohort (CRIC) study. Functional analysis of NH₃/NH₄ ⁺ transport was conducted in Xenopus oocytes expressing RhBG protein or mutants. NH₃ and NH₄ ⁺ transport was evaluated by electrophysiological measurements, including whole cell current, surface pH and intracellular pH. Our study identified six critical RhBG mutations associated with CKD. G86S and G86C inhibited the transport of NH₃; mutations G148R and G148W completely blocked transport of NH₃ and NH₄ ⁺, whereas T250A and T250S only inhibited NH₃ transport. Mutation T250M completely inhibited transport of both NH₃ and NH₄ ⁺. Our study identified critical rare non-synonymous single nucleotide polymorphisms in RhBG associated with CKD and elucidated the impact of these variants on NH₃/NH₄ ⁺ transport. These data are crucial to our understanding of how mutations can disrupt NH₃/NH₄ ⁺ transport, potentially affecting kidney function in CKD patients susceptible to acidosis. KEY POINTS: Acidosis and low urinary ammonium excretion contribute to poor outcomes in chronic kidney disease (CKD). This study investigates how the function of an ammonia transporter in renal collecting duct (RhBG) may contribute to CKD. Here, we report six rare RhBG mutations associated with CKD, identified using data from the Chronic Renal Insufficiency Cohort (CRIC) study. Using electrophysiological measurements, functional analysis in Xenopus oocytes showed that these RhBG mutations disrupt ammonia transport, with some mutations affecting only NH₃ transport, whereas others affect both NH₃ and NH₄ ⁺ transport. The results suggest that impaired ammonia transport by RhBG contributes to CKD, highlighting the need to understand mechanisms that link function (NH₃/NH₄ ⁺ and acid-base regulation) and genetic predisposition to CKD.