The Functional Characterization Study Of SLC12A3 Gene Mutation Causing Gitelman Syndrome In Two Pedigrees

BackgroundHypokalaemia is the most common electrolyte abnormality observed in clinical practice and is found in approximately 20% of hospital inpatients. Severe or prolonged potassium depletion can result in glucose intolerance and serious cardiac, renal, and neurologic dysfunction, including death. Hypokalaemia can be effectively corrected if detected in an incipient stage. However, patients with unexplained hypokalaemia are a considerable challenge for diagnosis.Gitelman Syndrome (GS, OMIM 263800) is one of the most frequently inherited causes of hypopatassium, and its prevalence is estimated to be ～25 per million. Patients most commonly present with symptoms of hypokalaemic metabolic alkalosis, hypomagnesemia and hypocalciuria without hypertension. Inherited in an autosomal recessive manner, GS is caused by loss-of-function mutations in the SLC12A3 (solute carrier family 12 member 3) gene (GenelD:6559; MIM:600968; GeneBank: NC000016.10), encoding the thiazide-sensitive, electroneutral Na+-Cl-cotransporter (NCC) of the distal convoluted tubule (DCT). NCC is a polypeptide of about 1000 amino acids, and the 2D-structure is predicted to contain 12 transmembrane domains and long intracellular carboxy-and short amino-termini. Moreover, GS has high genetic heterogeneity, lacking any correlation between the severity of symptoms and the type of mutation found in the SLC12A3 gene, identification of novel mutation and genotype-phenotype correlation analysis will provide further insights into the function of NCC and improve patient counselling. Further analysis of the mutation will doubtlessly assist in understanding the mechanism behind the phenotypic variability.ObjectiveHere, we aimed to investigate the clinical and genetic characteristics of two Chinese pedigrees and summarise the advance in GS genetics, diagnosis, and management.Subjects and MethodsTwo three-generation families with GS were identified and screened for mutations in the SLC12A3 gene. Genotype-phenotype correlations were analysed.ResultsThe two probands (A and B) were characterised by hypokalaemia, hypomagnesemia and hypocalciuria without hypertension. Complete DNA sequencing of the SLC12A3 gene revealed two novel compound heterozygous mutations (c.179C>T and c.234delG; c.486-490delTACGGinsA and c.1925G>A), which are predicted to drastically affect normal protein structure. The female members of the pedigrees showed mild to no phenotype, though they carried the same mutations as the probands. Moreover, proband B presented more severe symptoms than did proband A, which might be related to a lower serum magnesium level. During the 1-year follow-up, both probands showed satisfactory symptom improvement following the use of potassium and magnesium supplements.ConclusionOur findings strongly suggested that the two novel mutations in the SLC12A3 gene are the causative agents of GS, which may provide further insights into the function of this gene and help clinicians better understand this disorder.