A novel, dominant disease mechanism of distal renal tubular acidosis with specific variants in ATP6V1B1.

Background And Hypothesis: ATP6V1B1 encodes a subunit of the vacuolar H+-ATPase and pathogenic variants are associated with autosomal recessive distal renal tubular acidosis (dRTA) with deafness. Heterozygous variants predicted to affect a specific amino acid, Arg394, have been recurrently reported in dRTA but their significance has been unclear. We hypothesised that these variants are associated with a dominant disease mechanism.

Methods: Retrospective analysis of cases identified in our genetic laboratories and through European nephrology organisations. Data regarding demographics, clinical presentation, laboratory findings, hearing and imaging studies of kidneys were collected from the index patient and, if available, from other family members. The potential disease mechanism was investigated through structural modelling in silico.

Results: Twenty index patients in total were included, of which 19 carried the variant c.1181G>A; p.(Arg394Gln) and one c.1180C>G; p.(Arg394Gly). In 7 families, more than one member was affected and the variant segregated with the disease in those with available information (15 affected, 6 unaffected), except for the unaffected mother of 2 affected children, who was mosaic. In no patient was a second causative variant in trans identified. In 8 sporadic patients and 1 affected parent, the variant was confirmed to be de novo. Both variants are absent in gnomAD. Sensorineural hearing loss was reported in 8 of the 22 patients with available information. Structural modelling supports a crucial role for Arg394 in nucleotide binding.

Conclusion: We provide strong evidence for the pathogenicity of heterozygous variants affecting Arg394 and thus a novel inheritance modus for ATP6V1B1-associated dRTA. Clinically, this form differs from the recessive one by the lower prevalence of hearing loss. The prominent position of Arg394 in the nucleotide binding fold of the H+-ATPase structure is consistent with a dominant negative mechanism. Our findings inform the diagnosis and management of patients with dRTA and variants of Arg394.