The term "Bartter syndrome" encompasses a group of closely related inherited tubulopathies characterized by markedly reduced NaCl transport by the distal nephron. At present, five different genetic variants have been demonstrated. The majority of patients with so-called classic Bartter syndrome carry inactivating mutations of the CLCNKB gene encoding the basolateral ClC-Kb chloride channel (Bartter syndrome type III). The purpose of this study was to investigate the underlying mutation in cases of classic Bartter syndrome followed at our center. Ten patients, including two sisters, with clinical and biochemical features of classic Bartter syndrome were included in the mutational analysis. They originated from different regions of Spain with either Basque or Spanish ancestry. There was no history of consanguineous marriage in any of the kindreds. The parents and siblings of each patient, as well as a population of 300 healthy control adult subjects, were also analyzed. All ten patients were found to be homozygous for an identical missense mutation in the CLCNKB gene, substituting a threonine for an alanine at codon 204 (A204T) in the putative fifth transmembrane domain of the protein. None of the 300 control subjects were homozygous for the A204T allele. Overall, the A204T mutation was detected on 2/600 control chromosomes. Despite sharing a common mutation, the clinical manifestations of the syndrome in the patients varied from lack of symptoms to severe growth retardation. Demonstration of a point mutation within the CLCNKB gene as the apparently unique cause of Bartter syndrome type III in Spain is highly suggestive of a founder effect. Our results also support the lack of correlation between genotype and phenotype in this disease.

BackgroundPrimary distal renal tubular acidosis (dRTA) caused by mutations in the genes that codify for the H + −ATPase pump subunits is a heterogeneous disease with a poor phenotype-genotype correlation. Up to now, large cohorts of dRTA Tunisian patients have not been analyzed, and molecular defects may differ from those described in other ethnicities. We aim to identify molecular defects present in the ATP6V1B1, ATP6V0A4 and SLC4A1 genes in a Tunisian cohort, according to the following algorithm: first, ATP6V1B1 gene analysis in dRTA patients with sensorineural hearing loss (SNHL) or unknown hearing status. Afterwards, ATP6V0A4 gene study in dRTA patients with normal hearing, and in those without any structural mutation in the ATP6V1B1 gene despite presenting SNHL. Finally, analysis of the SLC4A1 gene in those patients with a negative result for the previous studies.Methods25 children (19 boys) with dRTA from 20 families of Tunisian origin were studied. DNAs were extracted by the standard phenol/chloroform method. Molecular analysis was performed by PCR amplification and direct sequencing.ResultsIn the index cases, ATP6V1B1 gene screening resulted in a mutation detection rate of 81.25%, which increased up to 95% after ATP6V0A4 gene analysis. Three ATP6V1B1 mutations were observed: one frameshift mutation (c.1155dupC; p.Ile386fs), in exon 12; a G to C single nucleotide substitution, on the acceptor splicing site (c.175-1G > C; p.?) in intron 2, and one novel missense mutation (c.1102G > A; p.Glu368Lys), in exon 11. We also report four mutations in the ATP6V0A4 gene: one single nucleotide deletion in exon 13 (c.1221delG; p.Met408Cysfs*10); the nonsense c.16C > T; p.Arg6*, in exon 3; and the missense changes c.1739 T > C; p.Met580Thr, in exon 17 and c.2035G > T; p.Asp679Tyr, in exon 19.ConclusionMolecular diagnosis of ATP6V1B1 and ATP6V0A4 genes was performed in a large Tunisian cohort with dRTA. We identified three different ATP6V1B1 and four different ATP6V0A4 mutations in 25 Tunisian children. One of them, c.1102G > A; p.Glu368Lys in the ATP6V1B1 gene, had not previously been described. Among deaf since childhood patients, 75% had the ATP6V1B1 gene c.1155dupC mutation in homozygosis. Based on the results, we propose a new diagnostic strategy to facilitate the genetic testing in North Africans with dRTA and SNHL.

IntroductionType III Bartter syndrome (BS) is an autosomal recessive renal tubule disorder caused by loss-of-function mutations in the CLCNKB gene, which encodes the chloride channel protein ClC-Kb. In this study, we carried out a complete clinical and genetic characterization in a cohort of 30 patients, one of the largest series described. By comparing with other published populations, and considering that 80% of our patients presented the p.Ala204Thr Spanish founder mutation presumably associated with a common phenotype, we aimed to test the hypothesis that allelic differences could explain the wide phenotypic variability observed in patients with type III BS.MethodsClinical data were retrieved from the referral centers. The exon regions and flanking intronic sequences of the CLCNKB gene were screened for mutations by polymerase chain reaction (PCR) followed by direct Sanger sequencing. Presence of gross deletions or duplications in the region was checked for by MLPA and QMPSF analyses.ResultsPolyuria, polydipsia and dehydration were the main common symptoms. Metabolic alkalosis and hypokalemia of renal origin were detected in all patients at diagnosis. Calciuria levels were variable: hypercalciuria was detected in 31% of patients, while 23% had hypocalciuria. Nephrocalcinosis was diagnosed in 20% of the cohort. Two novel CLCNKB mutations were identified: a small homozygous deletion (c.753delG) in one patient and a small deletion (c.1026delC) in another. The latter was present in compound heterozygosis with the already previously described p.Glu442Gly mutation. No phenotypic association was obtained regarding the genotype.ConclusionA poor correlation was found between a specific type of mutation in the CLCNKB gene and type III BS phenotype. Importantly, two CLCNKB mutations not previously described were found in our cohort.

• In most cases (90 %), inherited nephrogenic diabetes insipidus (NDI) is an X-linked disease, caused by mutations in the AVPR2 gene. • In rare occasions (10 %), it is caused by mutations in the AQP2 gene. What is new: • In this study, we report 10 novel mutations associated with NDI. • We have detected a high presence (50 %) of heterozygous carriers with clinical NDI symptoms.

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.

The MHC class I chain-related A gene (MICA) is expressed in gastrointestinal epithelium and functions as an immune activation signal under stress conditions. MICA protein binds to NKG2D, a receptor of gamma delta T cells containing the TCR variable region V(delta)1, which are the most abundant subset of T cells in the intestinal epithelium. Ingested gluten in patients with celiac disease (CD) may function as a stress signal for the epithelial cells, and could enhance MICA expression on their surface. In this study, we have analyzed MICA expression in intestinal biopsy specimens from newly diagnosed and treated CD patients and controls. Quantitative RT-PCR analysis did not show differences in MICA expression among the three groups. With these results, we conclude that overexpression of MICA does not seem to play an important role in the pathogenesis of CD, at least at the time of diagnosis.

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Hyperparathyroidism-jaw tumour syndrome (HPT-JT) is a rare variant of familial hyperparathyroidism, characterized by primary hyperparathyroidism (PHPT) due to one or multiple parathyroid adenomas, and benign tumours of the mandible and maxilla. It has an autosomal dominant pattern of inheritance, and is associated with mutations that deactivate the cell division cycle protein 73 homolog (CDC73) gene, also known as hyperparathyroidism 2 (HRPT2), located on the long arm of chromosome 1, that encodes for the tumour suppressor protein parafibromin. In the majority of cases, PHPT is the presenting symptom, but up to 30 % of HPT-JT cases initially present with an ossifying fibroma of the maxillofacial bones. HPT-JT may result in severe hypercalcemia-related complications and an elevated risk of parathyroid carcinoma. For this reason, early identification of the disease is important. We present the case of a 23-year-old woman who was found to have jaw tumours and was later diagnosed with PHPT. Genetic analysis revealed a novel mutation in exon 1 of CDC73. This report contributes to the understanding of the genetics of this rare syndrome. It also highlights the fact that HPT-JT should be considered and CDC73 mutation analysis should be performed in cases of early-onset PHPT associated with ossifying fibromas of the jaw.