Analysis Of CLCNKB Gene Mutation In Patients With Classic Bartter Syndrome

Background:Bartter syndrome (BS) is a group of symptoms that include hypokalaemic metabolic alkalosis, renal salt and water loss, hyperreninemic hyperaldosteronism and normal blood pressure.So far,six gene mutations in proteins regulating the sodium chloride transport in the thick ascending limb of Henle's loop have been described.TypeⅠ-ⅤBartter syndrome and Gitelman syndrome.Bartter syndrome typeⅠis caused by mutations of NKCC2.NKCC2 is encoded by the SLC12A1 gene.Bartter syndrome typeⅡis due to mutations of the KCNJ1 gene, encoding the inward-rectifier voltage-dependent potassium channel ROMK.Bartter syndrome typeⅢis caused by mutations of the CLCNKB gene, encoding a chloride channel protein CIC-Kb.Bartter syndrome type IV is found to be caused by mutations of the BSND gene. The BSND gene encodes protein'barttin'.BS type V is associated with activating mutations of the CASR gene.Gitelman syndrome is caused by mutations of the SLC12A3 gene, encoding the renal thiazide-sensitive sodium chloride co-transporter NCCT.TypeⅢBartter syndrome(Classic Bartter syndrome)is caused by mutations in the gene encoding the chloride channel ClC-Kb.cBS is diagnosed during infancy or childhood and leads to renal salt and water loss, polyuria.dehydration, muscular weakness,delayed growth.Most patients have normal calcium excretion rates and no medullary nephrocalcinosis.Some chilrens have a history of premature and hydramnios. The genotype-phenotype correlation in BS has been blurred by reports of several patients carrying mutations of the chloride channel CIC-Kb who displayed mixed clinical features that overlap with other phenotypes like aBS or GS.Because of phenotypic variability of TypeⅢBartter syndrome studies on the gene CLCNKB mutations might be of benefit to early diagnosis, effective therapy and prepotency.Objective:To understand the mutations of CLCNKB gene in classic Bartter syndrome patients and discuss the pathogenesis,we investigate the mutations in a patient with cBS.Methods:Genetic DNA was extracted from peripheral blood leucocytes of patients.The coding exons and intron—exon junctions of CLCNKB gene were amplyfied by polymerase chain reaction(PCR) and sequenced directly. Fifty unrelated subjects were selected to exclude the possibility of polymorphism.Results:1.Clinical and biochemical findings:The 4 months old child was diagnosed as Bartter syndrome in a local hospital. Symptoms include vomit, diarrhoea,fever,hypokalaemic metabolic alkalosis, renal salt loss,hyperreninemic hyperaldosteronism.The patient was treated with indomethacin 10mg/day,spironolactone 10 mg/day and potassium chloride supplementation.After 7 years,the child showed symptoms of polydipsia, polyuria, constipation,convulsiveseizure and growth retardation.She was 110 cm tall, weighted 21 kg and her blood pressure was 90/65mmHg.She also had hypokalaemia, with inappropriate urine K loss, and metabolic alkalosis.Both plasma aldosterone and renin levels were increased, which ruled out 'normotensive' primary hyperaldosteronism. A urine screen for diuretics also was negative. Renal function and ultrasound were normal.Her father and mother clinical and biochemical findings were normal.2.Genetic analyses:One heterozygous missense mutations (482T>G, L161R) in exon 4 was detected in the patient; Her mother had such abnormality and her father was normal.L161R has not been reported previously.We also found 8 coding single-nucleotide polymorphisms(cSNP) in CLCNKB gene.All these cSNPs have been reported. Conclusion:The L161R is identified for the firsttime. In this study,the discovery of mutations in CLCNKB gene not only provide valuable insight in to the pathogenesis of one patient with classic Bartter syndrome,but also improve the whole understanding of the disease.