Renal Tubular Acidosis, Distal, 3, With or Without Sensorineural Hearing Loss (dRTA-3)

Disease knowledge-base report MONDO:0011268 · OMIM #602722 · Gene: ATP6V0A4 (HGNC:865) · Category: Mendelian, autosomal recessive

Summary

Renal tubular acidosis, distal, type 3, with or without sensorineural hearing loss (dRTA-3) is a rare Mendelian, autosomal-recessive kidney tubular disorder caused by biallelic loss-of-function mutations in ATP6V0A4 on chromosome 7q34. ATP6V0A4 encodes the a4 subunit of the membrane-integral V0 domain of the vacuolar-type H⁺-ATPase (V-ATPase), a proton pump concentrated on the apical (luminal) membrane of α-intercalated cells (type A intercalated cells) in the renal collecting duct. When this pump fails, the distal nephron can no longer secrete protons into the tubular lumen, so the urine cannot be acidified below pH ~5.5 even during systemic acidosis. The result is a lifelong hyperchloremic, normal-anion-gap metabolic acidosis with hypokalemia, hypercalciuria, hypocitraturia, nephrocalcinosis, growth failure, and rickets. Because the identical pump also acidifies the endolymph of the inner ear, affected patients may additionally develop sensorineural hearing loss (SNHL) — historically thought to be late-onset (hence "with or without SNHL"), but now known to be able to appear in early childhood as well.

The disease is diagnosed biochemically (inappropriately alkaline urine, pH >5.5, during a normal-anion-gap metabolic acidosis, confirmed by ammonium-chloride acid-loading or furosemide/fludrocortisone testing) and molecularly (next-generation sequencing gene panels or whole-exome sequencing targeting SLC4A1, ATP6V1B1, ATP6V0A4, WDR72, FOXI1, and CA2). Treatment is lifelong oral alkali (sodium/potassium bicarbonate and citrate); a prolonged-release potassium citrate/potassium bicarbonate formulation (ADV7103 / Sibnayal) improves metabolic control, lowers lithogenic risk, and improves bone density, growth and quality of life relative to standard-of-care alkali. Correcting the acidosis does not reverse established hearing loss, so regular audiological follow-up is essential.

dRTA-3 sits within a genetically heterogeneous family of inherited dRTAs. ATP6V0A4 accounts for roughly 14–24 % of genetically solved cases in recent multicenter cohorts. Its closest genetic sibling, ATP6V1B1-associated dRTA (dRTA type 2 with early deafness, OMIM #267300), encodes the B1 subunit of the same pump and typically produces earlier and more frequent hearing loss; nevertheless, hearing status alone does not reliably distinguish the two genes, which is why molecular testing independent of audiometry is recommended. An Atp6v0a4 knockout mouse faithfully recapitulates the renal biochemistry and the deafness (with an absent endocochlear potential), and also reveals extrarenal a4 expression in bone, nose, eye and skin.

Section-by-Section Report

1. Disease Information

Overview. dRTA-3 is a primary (genetic) form of distal (type 1) renal tubular acidosis, defined by the inability of the distal nephron to maximally acidify the urine during systemic metabolic acidosis, owing to dysfunction of the α-intercalated cells of the collecting duct. It presents in infancy/early childhood with failure to thrive, polyuria, metabolic acidosis, hypokalemia and nephrocalcinosis, and may be accompanied by sensorineural hearing loss.

Key identifiers. - OMIM: #602722 (phenotype); gene ATP6V0A4 OMIM 605239 - MONDO: MONDO:0011268 - Gene / HGNC: ATP6V0A4, HGNC:865; NCBI Gene 50617; Ensembl ENSG00000105929; UniProt Q9HBG4; cytoband 7q34 - Orphanet: distal renal tubular acidosis, ORPHA:18 (parent term) - ICD-10: N25.89 (disorders resulting from impaired renal tubular function) — no dedicated dRTA-3 code; ICD-11: GB90.4 (renal tubular acidosis) - MeSH: Acidosis, Renal Tubular (D000141)

Synonyms / alternative names. Recessive distal renal tubular acidosis (rdRTA2); distal RTA with or without sensorineural hearing loss; RTADR (renal tubular acidosis, distal, with deafness); ATP6V0A4-related dRTA. The gene was originally named ATP6N1B and described as causing dRTA "with preserved hearing" (PMID: 10973252).

Source of information. This report is derived from aggregated disease-level resources — OMIM, published cohort studies and case series, functional/model-organism studies, and clinical trials — rather than from individual-patient EHR data.

2. Etiology

Primary cause — genetic. dRTA-3 is caused by biallelic (homozygous or compound-heterozygous) loss-of-function mutations in ATP6V0A4. Smith et al. (2000) identified the gene in dRTA kindreds, finding homozygous truncating (nonsense, deletion, splice-site) mutations in 8 of 9 kindreds with (initially) normal audiometry (PMID: 10973252). The gene "encodes an 840 amino acid novel kidney-specific isoform of ATP6N1A, the 116-kD non-catalytic accessory subunit of the proton pump." (Finding F001)

Genetic risk factors. - Causal variants: loss-of-function alleles in ATP6V0A4 (nonsense, frameshift, splice-site, and deleterious missense). See Section 4. - Modifier genes: genetic background modifies the hearing phenotype. In V-ATPase-deficient mice, a chromosome-13 modifier locus accounts for ~20 % of hearing-threshold variation (Tian et al. 2017, PMID: 28934385); the renal acidification defect, by contrast, is fully penetrant. (Finding F010)

Environmental / demographic risk factors. - Consanguinity / family history is the dominant demographic risk factor because the disorder is recessive: 23 of 26 kindreds were consanguineous in Stover et al. 2002 (PMID: 12414817), and 18 of 39 in Vargas-Poussou et al. 2006 (PMID: 16611712). (Finding F012) - Sex: no strong sex bias (≈52 % female in the European cohort), as expected for autosomal recessive inheritance (PMID: 30773598). - There are no established acquired/toxic causes of dRTA-3 itself; environmental exposures instead cause secondary/acquired dRTA that must be distinguished from the genetic disease (Section 13).

Protective factors. No specific genetic or environmental protective alleles are established for dRTA-3. The only "modifiers" documented act on the hearing phenotype (above). Early diagnosis and adequate alkali therapy are protective against complications (growth failure, CKD progression, stone disease) but do not modify disease occurrence.

Gene–environment interactions. None specifically documented for dRTA-3. The disease is essentially fully genetically determined; environmental factors (e.g., intercurrent illness, dietary acid load) influence the severity of decompensation and the ease of achieving metabolic control rather than causing the disease.

3. Phenotypes

Renal / systemic phenotypes (Findings F006, F005):

Watanabe (2018) summarizes: "Common clinical features of dRTA include vomiting, failure to thrive, polyuria, hypercalciuria, hypocitraturia, nephrocalcinosis, nephrolithiasis, growth delay, and rickets." (PMID: 30588151, Finding F006).

Sensorineural hearing loss (the defining "with or without" feature). In ATP6V0A4 disease, SNHL is less frequent and usually later-onset than in ATP6V1B1 disease. Priyadarshini 2025 reported SNHL in 22.2 % of ATP6V0A4 vs 61.5 % of ATP6V1B1 patients (PMID: 40232499, Finding F006); the Indian registry found SNHL "strongly associated with ATP6V1B1 variants (53.8 %)" (PMID: 42622870). However, SNHL can be congenital, early, or progressive — 7 ATP6V0A4 probands developed severe early SNHL between 2 months and 10 years (PMID: 16611712, Finding F008). The hearing loss is frequently associated with large vestibular aqueduct syndrome (LVAS/EVA) on imaging (PMID: 37121229, Finding F009).

Progression / severity. The renal acidification defect is stable and lifelong; CKD is slowly progressive. Hearing loss may be stable or progressive. Symptom severity is variable, driven partly by adequacy of metabolic control and (for hearing) genetic background.

Quality of life. dRTA and its treatment significantly impact QoL across education/work, social/family life, and emotional/physical well-being; treatment burden (frequent dosing, palatability) is a major contributor, and switching to twice-daily ADV7103 markedly improved QoL (mean satisfaction 9/10) (PMID: 35346296; PMID: 33635379, Finding F011).

4. Genetic / Molecular Information

Causal gene. ATP6V0A4 (a.k.a. ATP6N1B, ATP6N2, RTADR, VPP2), 7q34; gene OMIM 605239; disease OMIM #602722. Encodes the a4 subunit — an 840-amino-acid, kidney-enriched isoform of the 116-kD non-catalytic membrane subunit of the V-ATPase (Finding F001, F014).

Pathogenic variants. - Affected gene / IDs: ATP6V0A4, HGNC:865; UniProt Q9HBG4; Ensembl ENSG00000105929 (Finding F014). - Variant classification (ACMG/AMP): the majority of reported disease alleles are pathogenic / likely pathogenic truncating variants; deleterious missense variants also occur. - Variant types: nonsense, frameshift (deletions/insertions), splice-site, and missense. Smith 2000 found homozygous truncating mutations in 8/9 kindreds (PMID: 10973252). Vargas-Poussou 2006 reported 14 new + 5 recurrent ATP6V0A4 mutations across 21 families (PMID: 16611712). - Functional consequence: loss of function of the apical proton pump (Findings F004, F008). Batlle & Haque (2012): ATP6V1B1 and ATP6V0A4 mutations "cause loss of function of the apical H⁺-ATPase and autosomal recessive dRTA" (PMID: 23114896). - Origin: germline, biallelic. Not a somatic disorder. - Allele frequency: individual pathogenic alleles are rare in population databases (gnomAD); no single common founder allele is established for ATP6V0A4, although recurrent/founder alleles occur in consanguineous populations.

Modifier genes. Genetic background modifies the inner-ear phenotype (Chr-13 modifier locus in mice, ~20 % of hearing-threshold variance; Tian 2017 PMID: 28934385) (Finding F010).

Epigenetic information. No disease-specific DNA-methylation or histone-modification signatures are established for dRTA-3. Not applicable / not available.

Chromosomal abnormalities. None characteristic; dRTA-3 is a single-gene disorder, not a copy-number/structural syndrome.

Molecular assembly context. The a4 subunit is part of the membrane-integral V0 domain; a functional pump requires reversible assembly of the cytosolic V1 domain (ATP-hydrolytic, includes B1/ATP6V1B1) with V0 (proton-translocating). Eaton et al. 2024 showed the assembly factor Dmxl1/Rabconnectin-3A is required for V1–V0 assembly, and intercalated-cell-specific Dmxl1 knockout produces high urine pH like B1 knockouts: "the V-ATPase domains, V1 and VO, must assemble to produce a functional holoenzyme" (PMID: 38984989, Finding F014).

5. Environmental Information

• Environmental factors: none cause dRTA-3 (a monogenic disease). Environmental/toxic/drug exposures instead produce acquired dRTA (differential diagnosis, Section 13).
• Lifestyle factors: dietary acid load and fluid status influence decompensation and stone risk but do not cause the disease.
• Infectious agents: not applicable to genetic dRTA-3. (Note: infections such as visceral leishmaniasis can produce acquired acidification defects — a mimic, not the disease itself.)

6. Mechanism / Pathophysiology

Ordered causal chain (initiating lesion → clinical manifestation):

1. Biallelic loss-of-function mutation in ATP6V0A4 (germline) results in loss/dysfunction of the a4 subunit of the V0 domain of the vacuolar H⁺-ATPase.
2. Loss of a4 leads to failure of V0 assembly/function at the apical plasma membrane of renal α-intercalated cells, so a functional proton pump is not delivered to the luminal membrane (inferred to include impaired trafficking/assembly, by analogy to the Dmxl1 assembly requirement).
3. Loss of apical H⁺-ATPase activity results in inability to secrete protons (H⁺) into the collecting-duct lumen; the basolateral anion exchanger AE1 (SLC4A1) and cytosolic carbonic anhydrase II remain intact but are functionally uncoupled from proton export.
4. Impaired distal H⁺ secretion leads to failure to lower urinary pH below ~5.5 during systemic acidosis and reduced net acid excretion (impaired titratable acid + ammonium excretion).
5. Retained acid results in systemic hyperchloremic, normal-anion-gap metabolic acidosis.
6. Metabolic acidosis and impaired distal transport lead to secondary consequences: renal potassium wasting → hypokalemia; buffering of acid by bone → calcium and citrate mobilization → hypercalciuria + hypocitraturia; low urinary citrate and high urinary calcium → nephrocalcinosis / nephrolithiasis; chronic acid load in growing children → impaired bone mineralization → rickets, growth failure; chronic nephrocalcinosis/tubulointerstitial injury → progressive CKD.
7. Branch (inner ear): the same a4-containing V-ATPase acidifies endolymph in the cochlea/endolymphatic sac; its loss results in disrupted endolymph ion/pH homeostasis and loss of the endocochlear potential, leading to sensorineural hearing loss (often associated with enlarged vestibular aqueduct). Onset is variable (early to adult) and modified by genetic background.

Molecular pathways / biochemistry. The core defect is in acid–base transport, not a canonical signaling cascade. α-intercalated cells "secrete protons into the tubular lumen through H⁺-ATPases functionally coupled to the basolateral anion exchanger 1 (AE1)"; substrate H⁺ and HCO₃⁻ are generated by cytosolic carbonic anhydrase II (PMID: 23114896, Finding F004). "Dysfunction of intercalated cells in the collecting tubules accounts for all the known genetic causes of dRTA."

Cellular processes. Failure of regulated proton secretion / intracellular and luminal pH regulation; secondary tubulointerstitial injury/nephrocalcinosis. In the inner ear, additional pH-dependent processes are implicated (e.g., autophagic dysregulation of hair cells in a V-ATPase-deficient zebrafish model, PMID: 38277730).

Protein dysfunction. Loss of function of the a4 subunit; the multisubunit holoenzyme cannot translocate protons across the apical membrane (Finding F014).

Metabolic changes. Systemic acidosis; secondary bone mineral mobilization; hypocitraturia reflecting proximal citrate reabsorption driven by intracellular acidosis.

Biochemical abnormality (defining). An ion-transporter/proton-pump defect — the paradigmatic "biochemical abnormality" category for this disease.

Immune involvement. None in the primary genetic disease (immune-mediated α-intercalated-cell injury defines an acquired mimic — Sjögren's disease, Section 13).

Ontology suggestions. - GO (biological process): proton transmembrane transport (GO:1902600); regulation of intracellular pH (GO:0051453). - GO (cellular component): proton-transporting V-type ATPase, V0 domain (GO:0033179); vacuolar proton-transporting V-type ATPase complex (GO:0016471); apical plasma membrane (GO:0016324). - CL (cell types): renal alpha-intercalated cell (CL:1000715); kidney collecting duct intercalated cell (CL:1001432); cochlear hair cell. - UBERON: kidney collecting duct (UBERON:0001232); cochlea (UBERON:0001844); endolymphatic sac (UBERON:0002400); bone (UBERON:0002481). - CHEBI: proton/hydron (CHEBI:15378); bicarbonate (CHEBI:17544); citrate (CHEBI:16947); potassium (CHEBI:29103).

7. Anatomical Structures Affected

Organ level. - Primary: kidney (collecting duct / distal nephron) — UBERON:0001232, UBERON:0002113. - Secondary/other primary target: inner ear (cochlea, endolymphatic sac) — UBERON:0001844, UBERON:0002400. - Secondary involvement: bone/skeleton (rickets, osteopenia; UBERON:0002481); urinary tract (stones); growth axis (short stature). - Body systems: renal/urinary; auditory/nervous (sensory); musculoskeletal; endocrine-metabolic (acid–base).

Tissue and cell level. - Tissue: renal collecting-duct epithelium; cochlear sensory/supporting epithelium. - Cells: renal α-intercalated (type A intercalated) cells — CL:1000715 / CL:1001432; cochlear hair cells and endolymph-regulating epithelial cells. The Atp6v0a4 β-galactosidase reporter also revealed developmental expression in bone, nose, eye and skin (PMID: 22872862, Finding F003).

Subcellular level. Apical plasma membrane (GO:0016324); V-ATPase V0 domain (GO:0033179); the a4 subunit "localizes almost exclusively to the apical surface of α-intercalated cells" (PMID: 10973252, Finding F001).

Localization / lateralization. Renal involvement is bilateral (both kidneys); nephrocalcinosis is bilateral medullary. Hearing loss is typically bilateral, often with bilateral enlarged vestibular aqueducts.

8. Temporal Development

• Onset: typically congenital/infantile — median presentation age 0.5 years (range 0–54) in the European cohort (PMID: 30773598, Finding F012). Children with ATP6V0A4 (and ATP6V1B1) variants present earlier than those with SLC4A1/WDR72 (PMID: 42622870).
• Onset pattern: chronic, often with acute metabolic decompensation during intercurrent illness in infancy.
• Progression: the acidification defect is stable/lifelong; complications (nephrocalcinosis, CKD, short stature) are slowly progressive. CKD stage ≥2 rises from 35 % in children to 82 % in adults (PMID: 30773598, Finding F005).
• Hearing loss course: variable — congenital, early, or later-onset/progressive; regular audiological follow-up is essential (PMID: 37121229, Finding F009).
• Remission: none spontaneously; treatment controls (but does not cure) the biochemistry. Critical window: early diagnosis and alkali therapy protect growth and renal function.

9. Inheritance and Population

• Inheritance: autosomal recessive (PMID: 10973252, Finding F001, F012).
• Penetrance: complete for the renal acidification defect; variable expressivity/age of onset for SNHL.
• Consanguinity: major contributor — 23/26 kindreds (PMID: 12414817), 18/39 (PMID: 16611712) (Finding F012).
• Founder effects: recurrent alleles occur in specific/consanguineous populations; no single global founder allele established for ATP6V0A4.
• Carrier frequency / precise prevalence: not firmly established; dRTA overall is a rare disease (Orphanet ORPHA:18).
• Gene contribution: ATP6V0A4 accounts for ~14.2 % of solved dRTA in the Indian registry (PMID: 42622870) and ~22 % in another cohort; the overall genetic-diagnosis yield in dRTA is ~83 % (PMID: 30773598).
• Sex ratio: approximately equal (~52 % female), consistent with AR inheritance.
• Geographic distribution: worldwide; higher observed frequency in populations with high consanguinity. Genetic variant spectrum differs between Western and Asian cohorts (SLC4A1 dominant in India).

10. Diagnostics

Biochemical (core criteria). - Hallmark: inappropriately alkaline urine (pH >5.5) in the presence of a normal-anion-gap (hyperchloremic) metabolic acidosis (PMID: 19158053, Finding F007). - Confirmatory provocation tests: ammonium chloride (NH₄Cl) acid-loading test — dRTA patients keep urine pH >5.5 during induced acidosis (PMID: 21464016); furosemide (± fludrocortisone) test — normal controls lower urine pH <5.5, dRTA patients fail (sensitivity ~1.0, specificity ~0.89 vs NH₄Cl; PMID: 10862634). - Supporting labs: hypokalemia, hyperchloremia, low serum bicarbonate, hypercalciuria, hypocitraturia.

Imaging. Renal ultrasound/CT for nephrocalcinosis and stones; temporal-bone imaging (CT/MRI) for enlarged vestibular aqueduct in patients with hearing loss (PMID: 37121229).

Audiology. Pure-tone audiometry and auditory brainstem response (ABR); the mouse model shows elevated ABR thresholds and absent endocochlear potential (PMID: 22872862).

Genetic testing. NGS gene panels or whole-exome sequencing targeting SLC4A1, ATP6V1B1, ATP6V0A4, WDR72, FOXI1, CA2 confirm the molecular subtype; single-gene ATP6V0A4 testing where phenotype is suggestive. Mutation yield ~83 % (PMID: 30773598, Finding F007). Genetic testing is recommended independent of hearing status because hearing does not distinguish ATP6V0A4 from ATP6V1B1 (PMID: 16611712, Finding F008).

Clinical criteria / differential diagnosis. No formal society scoring system; diagnosis rests on the biochemical triad plus genetics. Differential includes acquired dRTA and other RTA subtypes (Section 13).

Screening. Cascade genetic testing of relatives once the familial variant is known; carrier testing for reproductive counseling.

11. Outcome / Prognosis

• Survival: generally normal life expectancy with treatment; dRTA-3 is not primarily life-limiting. (The knockout mouse dies without alkalinization, underscoring the importance of therapy.)
• Morbidity: substantial if untreated/undertreated — CKD stage ≥2 in 35 % of children and 82 % of adults; nephrocalcinosis 74–88 %; mean adult height SDS −0.57; stunting up to ~75 % in some cohorts (PMID: 30773598; PMID: 42622870, Findings F005, F006).
• Hearing: SNHL is irreversible once established; hence audiological monitoring and early hearing intervention.
• Prognostic factors: adequacy of metabolic control is the key modifiable prognostic factor — adequate control (normal bicarbonate + normocalciuria) was achieved in 51 %, more often in higher-GDP countries (67 % vs 23 %), and was associated with greater height and eGFR (PMID: 30773598, Finding F005). Genotype influences hearing and stone risk.
• Recovery: the renal biochemistry is fully correctable with alkali; complications are largely preventable with early, sustained control.

12. Treatment

Pharmacotherapy — mainstay: lifelong oral alkali (NCIT: alkalinizing agent). - Sodium bicarbonate / potassium bicarbonate / potassium citrate / sodium citrate. Median prescribed dose 1.9 (IQR 1.2–3.3) mEq/kg/day (PMID: 30773598, Finding F005). Potassium-based alkali is preferred to correct concomitant hypokalemia; citrate additionally reduces stone risk. - Potassium supplementation as needed for hypokalemia.

Prolonged-release combination (ADV7103 / Sibnayal — potassium citrate + potassium bicarbonate). EMA-authorized for dRTA. In an open-label non-inferiority trial (n=37), switching from standard of care raised the response rate from 43 % to 90 % and reduced urine Ca/citrate below the lithogenic threshold in 56 % of prior non-responders (PMID: 32712761, Finding F011). Over 24 months, bicarbonate/potassium were normal in 69–86 %/83–93 % of patients, adherence ≥75 % in 79 %, and QoL improved by ~89 % with only mild GI adverse events in 17 % (PMID: 33635379). Two years of ADV7103 "improved growth and increased spine BMD" (spine BMD z-score p=0.024) (PMID: 36529656).

Supportive / rehabilitative. - Hearing rehabilitation: hearing aids; cochlear implantation for severe/profound SNHL. Speech/language support in children. - Nutrition and growth monitoring; stone-prevention measures (hydration, citrate).

Advanced/experimental therapeutics. No gene, cell, or RNA-based therapy is approved or in trials for dRTA-3; management is entirely metabolic/supportive. Pharmacogenomics: not applicable.

Treatment strategy. Early diagnosis → titrate alkali to normalize plasma bicarbonate and urinary calcium/citrate → monitor growth, renal function, nephrocalcinosis, and hearing → multidisciplinary follow-up (nephrology, audiology, endocrinology/growth). NCIT suggestions: Sodium Bicarbonate (NCIT:C287), Potassium Citrate (NCIT:C47679), Potassium Bicarbonate, Cochlear Implantation.

13. Prevention

• Primary prevention: not possible for a monogenic disease; genetic counseling for at-risk (especially consanguineous) families, with carrier/cascade testing and options including prenatal or preimplantation genetic diagnosis once the familial variant is known.
• Secondary prevention: early biochemical diagnosis and prompt alkali therapy to prevent nephrocalcinosis, CKD progression, growth failure and bone disease.
• Tertiary prevention: sustained metabolic control (ADV7103/alkali) to prevent stones, preserve renal function and bone density; early hearing intervention.
• Immunization / public-health / environmental interventions: not applicable.

14. Other Species / Natural Disease

• Taxonomy / orthologs: mouse Atp6v0a4 (NCBI Gene 140470); the gene is evolutionarily conserved across vertebrates (zebrafish V-ATPase orthologs used as models).
• Model relevance: the Atp6v0a4 knockout mouse is the principal animal model (below). No well-characterized spontaneous companion-animal or wildlife dRTA-3 is established in OMIA for ATP6V0A4.
• Comparative biology: the α-intercalated-cell proton-secretion mechanism and V-ATPase subunit composition are conserved between human and mouse; the a4/B1 subunits serve the same kidney and inner-ear functions across species (the d2 subunit co-localizes with a4 in intercalated cells and with a3 in osteoclasts — PMID: 15800125).
• Transmission / zoonosis: not applicable (non-infectious genetic disease).

15. Model Organisms

Mouse — Atp6v0a4⁻/⁻ knockout (mammalian; principal model). Recapitulates the human disease: "Atp6v0a4(-/-) mice demonstrated severe metabolic acidosis, hypokalemia, and early nephrocalcinosis," and were "severely hearing-impaired, as shown by elevated auditory brainstem response thresholds and absent endocochlear potential" (PMID: 22872862, Finding F003). Mice die rapidly unless alkalinized; heterozygotes are normal until acid-challenged. A β-galactosidase reporter revealed developmental a4 expression in bone, nose, eye and skin in addition to kidney and inner ear. - Phenotype recapitulation: excellent for renal biochemistry and deafness/endocochlear-potential loss. - Limitations: high early lethality without alkali; extrarenal expression sites (bone/eye/nose/skin) not obviously symptomatic in humans; hearing phenotype is strongly strain/background dependent.

Mouse — Atp6v1b1 models (sibling gene). MRL-background Atp6v1b1 mutants show profound hearing loss with enlarged vestibular aqueducts, whereas B6-background knockouts hear normally; a Chr-13 modifier locus explains ~20 % of hearing-threshold variance — a model for the hearing-loss variability of dRTA (PMID: 28934385, Finding F010).

Zebrafish — atp6v1ba-deficient. Links V-ATPase-dependent pH imbalance to autophagic dysregulation of inner-ear hair cells (PMID: 38277730) — mechanistic model of the deafness component.

Mouse — intercalated-cell-specific Dmxl1 knockout. Demonstrates that V1–V0 assembly (Rabconnectin-3A/Dmxl1-dependent) is required for intercalated-cell V-ATPase function; KO mice have high urine pH like B1 knockouts (PMID: 38984989, Finding F014).

Resources: MGI (mouse), ZFIN (zebrafish), IMPC/IMSR for mutant strains.

Mechanistic Model (synthesis)

   ATP6V0A4 biallelic LOF mutation (germline, chr 7q34)
     │  results in
     ▼
   Loss of a4 subunit of V-ATPase V0 domain
     │  leads to (assembly/trafficking failure; V1–V0 must assemble)
     ▼
   No functional H+-ATPase at APICAL membrane of renal α-intercalated cells
     │  results in
     ▼
   Failure of luminal H+ secretion (AE1 + carbonic anhydrase II intact but uncoupled)
     │  leads to
     ▼
   Urine cannot acidify (pH >5.5) + ↓ net acid excretion
     │  results in
     ▼
   Hyperchloremic NORMAL-ANION-GAP METABOLIC ACIDOSIS  ──┬─► K+ wasting → HYPOKALEMIA
     │                                    ├─► bone buffering → HYPERCALCIURIA,
     │                                    │     HYPOCITRATURIA → NEPHROCALCINOSIS/STONES
     │                                    ├─► impaired bone mineralization → RICKETS,
     │                                    │     GROWTH FAILURE / SHORT STATURE
     │                                    └─► chronic tubulointerstitial injury → CKD
     │
   BRANCH (same pump, inner ear):
   Loss of a4 V-ATPase in cochlea / endolymphatic sac
     │  results in
     ▼
   Disrupted endolymph pH/ion homeostasis → LOSS OF ENDOCOCHLEAR POTENTIAL
   (± enlarged vestibular aqueduct)
     │  leads to
     ▼
   SENSORINEURAL HEARING LOSS (variable onset; modified by genetic background)

Upstream vs downstream: the mutation and pump loss are upstream; acidosis is the pivotal intermediate node; hypokalemia, stone disease, bone disease, CKD and hearing loss are downstream branches. Alkali therapy acts at the acidosis node — it corrects the renal/skeletal branches but cannot restore inner-ear proton pumping, explaining why hearing loss is not reversed.

Evidence Base

Limitations and Knowledge Gaps

1. Epidemiology is imprecise. No robust population prevalence, incidence, or ATP6V0A4 carrier frequency exists; cohorts are consanguinity-enriched and geographically skewed, so genotype proportions (14–24 %) are cohort-dependent.
2. Hearing-loss determinants are incompletely understood. Why some ATP6V0A4 patients develop early SNHL and others none is unexplained; modifier evidence is largely from mouse strains, and the human genetic modifiers are unmapped.
3. No dRTA-3-specific natural-history registry with long-term renal, auditory and skeletal endpoints stratified by genotype and treatment adequacy.
4. No omics data specific to dRTA-3 (transcriptomic/proteomic/metabolomic signatures) were identified; molecular-profiling sections are largely not applicable.
5. No causal/curative therapy. Gene- and cell-based approaches are absent; alkali corrects biochemistry but not hearing loss.
6. Genotype–phenotype correlation for individual ATP6V0A4 variants (e.g., missense vs truncating) is not well resolved.

Proposed Follow-up Experiments / Actions

1. Establish an ATP6V0A4-specific longitudinal registry capturing age-stratified audiometry, temporal-bone imaging (EVA), renal function, growth and treatment adequacy to define natural history and genotype–phenotype correlations.
2. Prospective audiological surveillance protocol from diagnosis to detect and time SNHL onset in ATP6V0A4 patients, testing whether early metabolic control alters hearing trajectory.
3. Functional variant characterization (in vitro assembly/trafficking/proton-pump assays; AlphaFold-guided structural interpretation) to reclassify VUS and correlate residual function with phenotype severity.
4. Map human modifiers of the hearing phenotype by GWAS/whole-genome analysis within dRTA cohorts, building on the murine Chr-13 modifier finding.
5. Real-world comparative-effectiveness study of ADV7103 vs conventional alkali on hard endpoints (CKD progression, stone events, final adult height, BMD) across health-economic settings.
6. Explore inner-ear-directed or gene-based strategies (e.g., AAV delivery of ATP6V0A4 to cochlea) using the knockout mouse/zebrafish models to address the currently irreversible hearing loss.

Consensus Answer

Renal tubular acidosis, distal, 3, with or without sensorineural hearing loss (dRTA-3; OMIM #602722, MONDO:0011268) is a rare autosomal-recessive disorder caused by biallelic loss-of-function mutations in ATP6V0A4 (7q34), encoding the a4 subunit of the apical vacuolar H⁺-ATPase of renal α-intercalated cells; loss of this proton pump abolishes distal urinary acidification, producing hyperchloremic normal-anion-gap metabolic acidosis with hypokalemia, hypercalciuria/hypocitraturia, nephrocalcinosis, growth failure and rickets, plus variable (often later-onset) sensorineural hearing loss because the same pump acidifies inner-ear endolymph. It is diagnosed by inappropriately alkaline urine (pH >5.5) during acidosis (confirmed by acid-loading/furosemide testing) plus NGS gene-panel sequencing, and managed lifelong with oral alkali (bicarbonate/citrate, including prolonged-release ADV7103/Sibnayal), which corrects the biochemistry and improves growth, bone and quality of life but does not reverse established hearing loss.

Artifacts

• OpenScientist final report
• OpenScientist final report

Reference Validation

Checked with linkml-reference-validator 0.2.1.

Quotes not found in the cited source

Searched the abstract, any retrieved full text, and the title. A quote drawn from a part of the paper that was not retrieved will appear here too, so check before treating one as invented:

Every one of these was searched against an abstract alone, with no full text retrieved - marked abstract only below. Where full text can be fetched, re-running with it will settle them; where the source publishes only a summary to PubMed, as GeneReviews chapters do, it will not, and the quote has to be checked by hand against the chapter itself.

• PMID:23114896 (abstract only): "cause loss of function of the apical H⁺-ATPase and autosomal recessive dRTA"
• closest text in source: "Mutations in ATP6V1B1, encoding the B-subtype unit of the apical H(+) ATPase, and ATP6V0A4, encoding the a-subtype unit, lead to the loss of function of the apical H(+) ATPase and are usually responsible for patients with autosomal recessive dRTA often associated with early or late sensorineural deafness"
• PMID:10973252 (abstract only): "localizes almost exclusively to the apical surface of α-intercalated cells"
• closest text in source: "Immunofluorescence studies in human kidney cortex revealed that ATP6N1B localizes almost exclusively to the apical surface of -intercalated cells"

Term Validation

Checked with linkml-term-validator 0.4.5, through the ols: adapter.

Terms the report names something else

These identifiers resolve, so nothing about them looks wrong, and the ontology calls them something unrelated to what the report calls them. That usually means the identifier is not the one the sentence needs:

• HP:0002900 (1 mention) - the report calls it "Lab abnormality"; HP calls it Hypokalemia
• HP:0000121 (1 mention) - the report calls it "Imaging/clinical"; HP calls it Nephrocalcinosis
• HP:0002150 (1 mention) - the report calls it "Lab abnormality"; HP calls it Hypercalciuria
• HP:0003128 (1 mention) - the report calls it "Lab abnormality"; HP calls it Lactic acidosis
• HP:0000787 (1 mention) - the report calls it "Clinical"; HP calls it Kidney stone
• HP:0002748 (1 mention) - the report calls it "Clinical/imaging"; HP calls it Rickets
• HP:0000103 (1 mention) - the report calls it "Symptom"; HP calls it Polyuria
• HP:0002013 (1 mention) - the report calls it "Symptom"; HP calls it Vomiting
• HP:0000407 (1 mention) - the report calls it "Clinical sign"; HP calls it Sensorineural hearing impairment
• HP:0012622 (1 mention) - the report calls it "Lab/clinical"; HP calls it Chronic kidney disease
• CHEBI:15378 (1 mention) - the report calls it "CHEBI: proton/hydron"; CHEBI calls it hydron**

Terms whose name is worth a second look

The report's name for these is recognisably related to the term's own name without being one of them. A loose paraphrase reads the same way as a citation of the wrong sibling term - and so does a related synonym, which the ontology records precisely because it names something adjacent rather than the same thing - so these are listed rather than judged:

• HP:0008341 (1 mention) - the report calls it "distal RTA"; HP calls it Distal renal tubular acidosis
• HP:0500018 (1 mention) - the report calls it "abnormal urine pH"; HP calls it Abnormal cardiac exercise stress test, and lists "Abnormal exercise test" among its other names
• UBERON:0001232 (2 mentions) - the report calls it "UBERON: kidney collecting duct"; UBERON calls it collecting duct of renal tubule**, and lists "kidney collecting duct" among its other names

Prefixes with no resolver

Terms carrying these prefixes were not checked either way, because no configured ontology covers them. An unrecognised prefix may name an ontology this run could not reach as easily as one that does not exist, so nothing here is evidence of fabrication: ORPHA.