A novel homozygous mutation (p.N958K) of SLC12A3 in Gitelman syndrome is associated with endoplasmic reticulum stress.

PURPOSE

Gitelman syndrome (GS) is an autosomal recessive renal tubular disease that arises as a consequence of mutations in the SLC12A3 gene, which codes for an Na-Cl cotransporter (NCC) in distal renal tubules. This study was designed to explore the mutations associated with GS in an effort to more fully understand the molecular mechanisms governing GS.

METHODS

We analyzed SLC12A3 mutations in a pedigree including a 42-year-old male with GS as well as four related family members over three generations using Sanger and next generation sequencing approaches. We additionally explored the functional ramifications of identified mutations using both Xenopus oocytes and the HEK293T cell line.

RESULTS

We found that the subject with GS exhibited characteristic symptoms including sporadic thirst, fatigue, excess urination, and substantial hypokalemia and hypocalciuria, although magnesium levels were normal. Other analyzed subjects in this pedigree had normal laboratory findings and did not exhibit clear signs of GS. Sequencing analyses revealed that the GS subject exhibited a homozygous missense mutation (c.2874C > G, p.N958K) in exon 24 of SLC12A3. Both parents of this GS subject, as well as his older brother and daughter all exhibited heterozygous mutations at this same site. Functional analyses in Xenopus oocytes indicated that this mutated SLC12A3 gene encodes a protein which fails to mediate normal sodium transport, and when this mutant gene was expressed in HEK293T cells, we observed significant increases in endoplasmic reticulum (ER)-stress pathway activation.

CONCLUSION

The p.N958K mutation in exon 24 of SLC12A3 can trigger GS at least in part via enhancing ER stress responses.