Novel mutations in the thiazide-sensitive NaCl cotransporter gene in patients with Gitelman syndrome with predominant localization to the C-terminal domain

Abstract

Gitelman syndrome (familial hypokalemia-hypomagnesemia syndrome) is an autosomal recessive inherited renal disorder characterized by defective tubular reabsorption of magnesium and potassium. In this study a group of 18 unrelated and 2 related Gitelman patients, collected from six different countries have been screened for mutations in the human thiazide-sensitive sodium-chloride cotransporter (SLC12A3) gene. Fourteen novel SLC12A3 mutations are presented along with six mutations described earlier, and three neutral polymorphisms. Among the tested patients are two who carry a total of three heterozygous SLC12A3 mutations. Two-thirds of the total number of mutant SLC12A3 alleles are amino acid substitutions. Most SLC12A3 gene mutations, 14 out of a total of 20, are localized at the intracellular carboxy-terminal domain of the NCCT protein. The pathogenicity of individual SLC12A3 mutations is based upon their predicted effect on SLC12A3 protein, and segregation in family members. Evolutionary conservation of substituted amino acid residues and their frequency in control chromosomes is presented. Identical mutations have been found in Gitelman families from different geographical origin, suggesting ancient mutations originating from a common ancestor. As yet, we have not found any evidence for a possible genotype-phenotype correlation.

Gitelman’s Syndrome Associated with Chondrocalcinosis: A Case Study from the Azores Islands (Portugal)

“…The S615L identified in this study was previously described by Cruz and co-workers [18] in a study involved 36 kindreds from the United States, Canada and England and later reported in a study by Syrén et al [22]. Although the SLC12A3 variations reported in previous studies are distributed throughout the whole protein [4,23], the study of Lemmink (1998) indicates that the carboxyterminal end represents a hot spot for variations [4]. S615L is located at the intracellular C-terminal end of the SLC12A3 protein.…”

“…The assumption that GS is caused by a defect in the NCCT cotransporter in the renal distal tubule has been proven by the identification of numerous variations in the SLC12A3 gene in patients with GS [1,4,19,21]. In the present study the specific involvement of this cotransporter in the etiology of this disorder is further substantiated by the finding that the proband is homozygous for the S615L variation.…”

“…S615L is located at the intracellular C-terminal end of the SLC12A3 protein. It is conceivable that structural alterations due to SLC12A3 variations in the C-terminal domain interfere with phosphorylation of the NCCT protein and as such with its regulation [4].…”

“…At present, according to the Human Gene Mutation Database (http:// www.hgmd.cf.ac.uk/), more than 100 different variants have been identified in patients with GS. They are missense, non-sense, frameshift, and splice-site variations and are scattered throughout the transporter protein with a possible clustering of variations in the carboxy-terminal tail [4].…”

Rare independent mutations in renal salt handling genes contribute to blood pressure variation

“…In addition, we included one further variant in NCCT found once in FHS, R861C, which has previously been reported as disease-causing 23,24 and was found in 4 of our European Caucasian GS subjects (homozygous in 1). This non-conservative substitution is at a position conserved among all vertebrates.…”