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Transporter Information:
Name: ATPase, H+ transporting, lysosomal V0 subunit a isoform 4
Symbol: ATP6V0A4
TC: 3.A.2.2.3
Locations: 7q33-34
Aliases: RDRTA2, VPP2, RTADR, a4, Vph1, Stv1, HGNC:867, HGNC:10465
GenBank: AF245517
Swiss-Prot: Q9HBG4
Accession Number: NM_130841
Old Name: ATPase, H+ transporting, lysosomal (vacuolar proton pump) non-catalytic accessory protein 1B
PubMed (10577919): Karet FE, Finberg KE, Nayir A, Bakkaloglu A, Ozen S, Hulton SA, Sanjad SA,Al-Sabban EA, Medina JF, Lifton RP. Localization of a gene for autosomal recessive distal renal tubular acidosiswith normal hearing (rdRTA2) to 7q33-34.Am J Hum Genet. 1999 Dec;65(6):1656-65. PMID: 10577919 [PubMed - indexed for MEDLINE]

Failure of distal nephrons to excrete excess acid results in the "distal renal tubular acidoses" (dRTA). Early childhood features of autosomal recessive dRTA include severe metabolic acidosis with inappropriately alkaline urine, poor growth, rickets, and renal calcification. Progressive bilateral sensorineural hearing loss (SNHL) is evident in approximately one-third of patients. We have recently identified mutations in ATP6B1, encoding the B-subunit of the collecting-duct apical proton pump, as a cause of recessive dRTA with SNHL. We now report the results of genetic analysis of 13 kindreds with recessive dRTA and normal hearing. Analysis of linkage and molecular examination of ATP6B1 indicated that mutation in ATP6B1 rarely, if ever, accounts for this phenotype, prompting a genomewide linkage search for loci underlying this trait. The results strongly supported linkage with locus heterogeneity to a segment of 7q33-34, yielding a maximum multipoint LOD score of 8.84 with 68% of kindreds linked. The LOD-3 support interval defines a 14-cM region flanked by D7S500 and D7S688. That 4 of these 13 kindreds do not support linkage to rdRTA2 and ATP6B1 implies the existence of at least one additional dRTA locus. These findings establish that genes causing recessive dRTA with normal and impaired hearing are different, and they identify, at 7q33-34, a new locus, rdRTA2, for recessive dRTA with normal hearing.

PubMed (10973252): Smith AN, Skaug J, Choate KA, Nayir A, Bakkaloglu A, Ozen S, Hulton SA,Sanjad SA, Al-Sabban EA, Lifton RP, Scherer SW, Karet FE. Mutations in ATP6N1B, encoding a new kidney vacuolar proton pump 116-kDsubunit, cause recessive distal renal tubular acidosis with preserved hearing.Nat Genet. 2000 Sep;26(1):71-5. PMID: 10973252 [PubMed - indexed for MEDLINE]

The multi-subunit H+-ATPase pump is present at particularly high density on the apical (luminal) surface of -intercalated cells of the cortical collecting duct of the distal nephron, where vectorial proton transport is required for urinary acidification. The complete subunit composition of the apical ATPase, however, has not been fully agreed upon. Functional failure of -intercalated cells results in a group of disorders, the distal renal tubular acidoses (dRTA), whose features include metabolic acidosis accompanied by disturbances of potassium balance, urinary calcium solubility, bone physiology and growth. Mutations in the gene encoding the B-subunit of the apical pump (ATP6B1) cause dRTA accompanied by deafness. We previously localized a gene for dRTA with preserved hearing to 7q33-34 (ref. 4). We report here the identification of this gene, ATP6N1B, which encodes an 840 amino acid novel kidney-specific isoform of ATP6N1A, the 116-kD non-catalytic accessory subunit of the proton pump. Northern-blot analysis demonstrated ATP6N1B expression in kidney but not other main organs. Immunofluorescence studies in human kidney cortex revealed that ATP6N1B localizes almost exclusively to the apical surface of -intercalated cells. We screened nine dRTA kindreds with normal audiometry that linked to the ATP6N1B locus, and identified different homozygous mutations in ATP6N1B in eight. These include nonsense, deletion and splice-site changes, all of which will truncate the protein. Our findings identify a new kidney-specific proton pump 116-kD accessory subunit that is highly expressed in proton-secreting cells in the distal nephron, and illustrate its essential role in normal vectorial acid transport into the urine by the kidney.

 >Q9HBG4|VPP4_HUMAN Vacuolar proton translocating ATPase 116 kDa subunit a isoform 4 - Homo sapiens (Human).