Genetics of Type III Bartter Syndrome in Spain, Proposed Diagnostic Algorithm

Abstract

The p.Ala204Thr mutation (exon 7) of the CLCNKB gene is a "founder" mutation that causes most of type III Bartter syndrome cases in Spain. We performed genetic analysis of the CLCNKB gene, which encodes for the chloride channel protein ClC-Kb, in a cohort of 26 affected patients from 23 families. The diagnostic algorithm was: first, detection of the p.Ala204Thr mutation; second, detecting large deletions or duplications by Multiplex Ligation-dependent Probe Amplification and Quantitative Multiplex PCR of Short Fluorescent Fragments; and third, sequencing of the coding and flanking regions of the whole CLCNKB gene. In our genetic diagnosis, 20 families presented with the p.Ala204Thr mutation. Of those, 15 patients (15 families) were homozygous (57.7% of overall patients). Another 8 patients (5 families) were compound heterozygous for the founder mutation together with a second one. Thus, 3 patients (2 siblings) presented with the c. -19-?_2053+? del deletion (comprising the entire gene); one patient carried the p.Val170Met mutation (exon 6); and 4 patients (3 siblings) presented with the novel p.Glu442Gly mutation (exon 14). On the other hand, another two patients carried two novel mutations in compound heterozygosis: one presented the p.Ile398_Thr401del mutation (exon 12) associated with the c. -19-?_2053+? del deletion, and the other one carried the c.1756+1G>A splice-site mutation (exon 16) as well as the already described p.Ala210Val change (exon 7). One case turned out to be negative in our genetic screening. In addition, 51 relatives were found to be heterozygous carriers of the described CLCNKB mutations. In conclusion, different mutations cause type III Bartter syndrome in Spain. The high prevalence of the p.Ala204Thr in Spanish families thus justifies an initial screen for this mutation. However, should it not be detected further investigation of the CLCNKB gene is warranted in clinically diagnosed families.

Poor phenotype-genotype association in a large series of patients with Type III Bartter syndrome

“…Total DNA was extracted from EDTA-preserved peripheral blood leukocytes by the QIAamp ® DNA Blood Mini Kit (QIAGEN) method. The exon regions, promoter (described by SwitchGear Genomics) and flanking intronic sequences of the CLCNKB gene (Ensembl identifiers: gene ENSG00000184908; transcript, ENST00000375679) were screened for mutations by polymerase chain reaction (PCR) followed by direct sequencing (primer sequences and the strategy used to specifically amplify the exons of the CLCNKB gene were published previously [ 9 ]).…”

“…A diagnostic algorithm based on previous experiences was used: first, detection of the p.Ala204Thr Spanish founder mutation [ 2 , 8 ]; second, detection of large deletions or duplications by MLPA and QMPSF; and third, sequencing of the rest of the coding and flanking regions of the whole CLCNKB gene [ 9 ].…”

Bartter syndrome: causes, diagnosis, and treatment

“…44 More than 75 mutations in the CLCNKB gene have been described, and the effect of the kind of mutation in the phenotype is not clearly related. 45 However, large deletions were observed to be more frequent in patients with early-onset and severe phenotypes. Some authors defend the hypothesis that phenotypic heterogeneity could be due to various degrees of compensation through alternative basolateral chloride efflux.…”

An Adult Case of Bartter Syndrome Type III Presenting with Proteinuria

“…The histologic and molecular features of BS have been well described in the literature [ 3 , 5 , 6 ], and histologic findings of BS consistently show juxtaglomerular hyperplasia, interstitial fibrosis and nephrocalcinosis. Juxtaglomerular hyperplasia is a characteristic finding but is not a necessary finding for diagnosis.…”