Stéphane Benoit

Mutation Update of the CLCN5 Gene Responsible for Dent Disease 1

Dent disease is a rare X‐linked tubulopathy characterized by low molecular weight proteinuria, hypercalciuria, nephrocalcinosis and/or nephrolithiasis, progressive renal failure, and variable manifestations of other proximal tubule dysfunctions. It often progresses over a few decades to chronic renal insufficiency, and therefore molecular characterization is important to allow appropriate genetic counseling. Two genetic subtypes have been described to date: Dent disease 1 is caused by mutations of the CLCN5 gene, coding for the chloride/proton exchanger ClC‐5; and Dent disease 2 by mutations of the OCRL gene, coding for the inositol polyphosphate 5‐phosphatase OCRL‐1. Herein, we review previously reported mutations (n = 192) and their associated phenotype in 377 male patients with Dent disease 1 and describe phenotype and novel (n = 42) and recurrent mutations (n = 24) in a large cohort of 117 Dent disease 1 patients belonging to 90 families. The novel missense and in‐frame mutations described were mapped onto a three‐dimensional homology model of the ClC‐5 protein. This analysis suggests that these mutations affect the dimerization process, helix stability, or transport. The phenotype of our cohort patients supports and extends the phenotype that has been reported in smaller studies.

Hodgkin's disease following steroid-resistant idiopathic nephrotic syndrome

We share Dr. Alons concern that the difference in incidence of proteinuria in the two groups could affect our conclusions. Separate comparisons were made for proteinuria of 1 3 and >3 g/1.73 m 2 per day because heavy proteinuria may indicate a worse prognosis. Dr. Alon is correct that, based on proteinuria > 1 g/1.73 m 2 per day alone as a prognostic factor, the treatment group appears to be less severely affected than the control group. However, proteinuria in IgA nephropathy may vary considerably with follow-up, making this a potentially confusing single prognostic factor. A second criterion for treatment in our study was the presence of glomerulosclerosis and/or interstitial fibrosis on initial renal biopsy. The presence of sclerosis in 20% or more of the glomeruli in the initial biopsy of a patient with lgA nephropathy may be the single best predictor of a poor prognosis [1]. Our patients with minimal proteinuria all had glomerular sclerosis in more than 20% of the glomeruli and/or associated interstitial fibrosis. Thus in this respect the treated and control patients were well matched and the benign course of treated patients suggests that prednisone is beneficial. 395

Structure-function analyses of metal-binding sites of HypA reveal residues important for hydrogenase maturation in Helicobacter pylori

The nickel-containing enzymes of Helicobacter pylori, urease and hydrogenase, are essential for efficient colonization in the human stomach. The insertion of nickel into urease and hydrogenase is mediated by the accessory protein HypA. HypA contains an N-terminal nickel-binding site and a dynamic structural zinc-binding site. The coordination of nickel and zinc within HypA is known to be critical for urease maturation and activity. Herein, we test the hydrogenase activity of a panel of H. pylori mutant strains containing point mutations within the nickel- and zinc-binding sites. We found that the residues that are important for hydrogenase activity are those that were similarly vital for urease activity. Thus, the zinc and metal coordination sites of HypA play similar roles in urease and hydrogenase maturation. In other pathogenic bacteria, deletion of hydrogenase leads to a loss in acid resistance. Thus, the acid resistance of two strains of H. pylori containing a hydrogenase deletion was also tested. These mutant strains demonstrated wild-type levels of acid resistance, suggesting that in H. pylori, hydrogenase does not play a role in acid resistance.

Site-directed mutagenesis of Campylobacter concisus respiratory genes provides insight into the pathogen’s growth requirements

Campylobacter concisus is an emerging human pathogen found throughout the entire human oral-gastrointestinal tract. The ability of C. concisus to colonize diverse niches of the human body indicates the pathogen is metabolically versatile. C. concisus is able to grow under both anaerobic conditions and microaerophilic conditions. Hydrogen (H2) has been shown to enhance growth and may even be required. Analysis of several C. concisus genome sequences reveals the presence of two sets of genes encoding for distinct hydrogenases: a H2-uptake-type (“Hyd”) complex and a H2-evolving hydrogenase (“Hyf”). Whole cells hydrogenase assays indicate that the former (H2-uptake) activity is predominant in C. concisus, with activity among the highest we have found for pathogenic bacteria. Attempts to generate site-directed chromosomal mutants were partially successful, as we could disrupt hyfB, but not hydB, suggesting that H2-uptake, but not H2-evolving activity, is an essential respiratory pathway in C. concisus. Furthermore, the tetrathionate reductase ttrA gene was inactivated in various C. concisus genomospecies. Addition of tetrathionate to the medium resulted in a ten-fold increase in cell yield for the WT, while it had no effect on the ttrA mutant growth. To our knowledge, this is the first report of mutants in C. concisus.

An antenatal hyper-echogenic colon: answer

1. Hyper-echogenic colon at the third trimester of pregnancy in this consanguineous couple may indicate cystinuria, all the more because there is a familial history of lithiasis and renal failure. 2. Amniocentesis was performed at 36 weeks of gestation. Liver function tests and karyotype were normal. An amino acid assay was performed on the amniotic fluid. The results were compatible with cystinuria.