Mutations in the gene encoding the kidney anion exchanger 1 (kAE1) can lead to distal renal tubular acidosis (dRTA). dRTA mutations reported within the carboxyl (C)-terminal tail of kAE1 result in apical mis-targeting of the exchanger in polarized renal epithelial cells.
Mutations in adenosine triphosphate ATP6V1 (B1 H<sup>+</sup>-ATPase subunit), ATPV0A4 (a4 H<sup>+</sup>-ATPase subunit), SLC4A1 (anion exchanger 1), and FOXI1 (forkhead transcription factor) cause distal renal tubular acidosis type I. Carbonic anhydrase II mutations affect several nephron segments and give rise to a mixed proximal and distal phenotype.
In patients with inherited distal renal tubular acidosis (dRTA), pendrin abundance in urinary exosomes was greatly reduced and did not change upon oral NH<sub>4</sub>Cl loading.
The genomic deletion reported here is firstly, the only reported example of a whole gene deletion to underlie Distal Renal Tubular Acidosis, where the clinical phenotype is indistinguishable from that of other patients with ATP6V1B1 mutations; secondly, this is the first reported example of a human VAX2 mutation and associated ocular phenotype, supporting speculation in the literature that VAX2 is important for correct retinal functioning.
The distribution of patients according to HRTD was as follows: 45.6% distal renal tubular acidosis (dRTA), 26.6% proximal RTA (pRTA), 3.5% type IV RTA, 21.7% Bartter's syndrome, and 2.6% Gitelman's syndrome.
The distribution of patients according to HRTD was as follows: 45.6% distal renal tubular acidosis (dRTA), 26.6% proximal RTA (pRTA), 3.5% type IV RTA, 21.7% Bartter's syndrome, and 2.6% Gitelman's syndrome.
These results show that functional dRTA mutants are retained in the ER due to their interaction with molecular chaperones, particularly calnexin, and that disruption of these interactions can promote their escape from the ER and cell surface rescue.
We propose that SLC26A7 dysfunction should be investigated as a potential cause of unexplained distal renal tubular acidosis or decreased gastric acid secretion in humans.
Elevated urinary RBP (>0.017) and albumin < (10 x RBP) + 2 identified all patients with the LMWP of Dent's disease and clearly distinguished their LMWP from that of dRTA and GN.
The biosynthesis and trafficking of kAE1 containing a novel recessive missense dRTA mutation (kAE1 S773P) was studied in transiently transfected HEK-293 cells, expressing the mutant alone or in combination with wild-type kAE1 or another recessive mutant, kAE1 G701D.
The effect of an 11-amino-acid C-terminal dRTA truncation mutation (901 stop) on the expression of kidney AE1 (kAE1) and erythroid AE1 was examined in transiently transfected HEK-293 cells.
Here, we present kidney tissues from dRTA-affected siblings heterozygous for kAE1G609R, characterized by predominant absence rather than mistargeting of kAE1 in intercalated cells.
Our data unveil the molecular mechanism of Golgi retention of kAE1G701D and suggest that disruption of the COPI-kAE1G701D interaction could be a therapeutic strategy to treat dRTA caused by this mutant.
The promoter regions of the kAE1 gene with the minor allele A at rs999716 downstream of the TATA box showed reduced promoter activities compared that with the major allele G. Patients with the A allele at rs999716 may express less kAE1 mRNA and protein in the intercalated cells, developing incomplete dRTA.
Thus impaired trafficking of the kAE1G701D and A858D mutants would lead to a profound decrease in functional kAE1 at the basolateral membrane of alpha-intercalated cells in the distal nephron of the patients with dRTA.
Therefore, compound heterozygous patients expressing both recessive mutants (G701D/S773P) likely developed dRTA due to the lack of a functional kAE1 at the basolateral surface of alpha-intercalated cells.
Individuals heterozygous with wild-type (WT) kAE1 either did not display any symptoms of dRTA (DeltaV850/WT) or displayed a mild incomplete form of dRTA (A858D/WT), while compound heterozygotes (DeltaV850/A858D) had dRTA.
Heterozygotes with SAO are able to acidify their urine, without symptoms of dRTA (distal renal tubular acidosis) that can be associated with mutations in kAE1.
The biosynthesis and trafficking of kAE1 containing a novel recessive missense dRTA mutation (kAE1S773P) was studied in transiently transfected HEK-293 cells, expressing the mutant alone or in combination with wild-type kAE1 or another recessive mutant, kAE1G701D.