Hubert Nivet

Mutations in INVS encoding inversin cause nephronophthisis type 2, linking renal cystic disease to the function of primary cilia and left-right axis determination

Nephronophthisis (NPHP), an autosomal recessive cystic kidney disease, leads to chronic renal failure in children. The genes mutated in NPHP1 and NPHP4 have been identified, and a gene locus associated with infantile nephronophthisis (NPHP2) was mapped. The kidney phenotype of NPHP2 combines clinical features of NPHP and polycystic kidney disease (PKD). Here, we identify inversin (INVS) as the gene mutated in NPHP2 with and without situs inversus. We show molecular interaction of inversin with nephrocystin, the product of the gene mutated in NPHP1 and interaction of nephrocystin with β-tubulin, a main component of primary cilia. We show that nephrocystin, inversin and β-tubulin colocalize to primary cilia of renal tubular cells. Furthermore, we produce a PKD-like renal cystic phenotype and randomization of heart looping by knockdown of invs expression in zebrafish. The interaction and colocalization in cilia of inversin, nephrocystin and β-tubulin connect pathogenetic aspects of NPHP to PKD, to primary cilia function and to left-right axis determination.

Mutations in complement C3 predispose to development of atypical hemolytic uremic syndrome

Atypical hemolytic uremic syndrome (aHUS) is a disease of complement dysregulation. In approximately 50% of patients, mutations have been described in the genes encoding the complement regulators factor H, MCP, and factor I or the activator factor B. We report here mutations in the central component of the complement cascade, C3, in association with aHUS. We describe 9 novel C3 mutations in 14 aHUS patients with a persistently low serum C3 level. We have demonstrated that 5 of these mutations are gain-of-function and 2 are inactivating. This establishes C3 as a susceptibility factor for aHUS.

The ciliary gene RPGRIP1L is mutated in cerebello-oculo-renal syndrome (Joubert syndrome type B) and Meckel syndrome

Cerebello-oculo-renal syndrome (CORS), also called Joubert syndrome type B, and Meckel (MKS) syndrome belong to the group of developmental autosomal recessive disorders that are associated with primary cilium dysfunction. Using SNP mapping, we identified missense and truncating mutations in RPGRIP1L (KIAA1005) in both CORS and MKS, and we show that inactivation of the mouse ortholog Rpgrip1l (Ftm) recapitulates the cerebral, renal and hepatic defects of CORS and MKS. In addition, we show that RPGRIP1L colocalizes at the basal body and centrosomes with the protein products of both NPHP6 and NPHP4, known genes associated with MKS, CORS and nephronophthisis (a related renal disorder and ciliopathy). In addition, the RPGRIP1L missense mutations found in CORS individuals diminishes the interaction between RPGRIP1L and nephrocystin-4. Our findings show that mutations in RPGRIP1L can cause the multiorgan phenotypic abnormalities found in CORS or MKS, which therefore represent a continuum of the same underlying disorder.

Differential Impact of Complement Mutations on Clinical Characteristics in Atypical Hemolytic Uremic Syndrome

Mutations in factor H (CFH), factor I (IF), and membrane cofactor protein (MCP) genes have been described as risk factors for atypical hemolytic uremic syndrome (aHUS). This study analyzed the impact of complement mutations on the outcome of 46 children with aHUS. A total of 52% of patients had mutations in one or two of known susceptibility factors (22, 13, and 15% of patients with CFH, IF, or MCP mutations, respectively; 2% with CFH+IF mutations). Age <3 mo at onset seems to be characteristic of CFH and IF mutation-associated aHUS. The most severe prognosis was in the CFH mutation group, 60% of whom reached ESRD or died within <1 yr. Only 30% of CFH mutations were localized in SCR20. MCP mutation-associated HUS has a relapsing course, but none of the children reached ESRD at 1 yr. Half of patients with IF mutation had a rapid evolution to ESRD, and half recovered. Plasmatherapy seemed to have a beneficial effect in one third of patients from all groups except for the MCP mutation group. Only eight (33%) of 24 kidney transplantations that were performed in 15 patients were successful. Graft failures were due to early graft thrombosis (50%) or HUS recurrence. In conclusion, outcome of HUS in patients with CFH mutation is catastrophic, and posttransplantation outcome is poor in all groups except for the MCP mutation group. New therapies are urgently needed, and further research should elucidate the unexplained HUS group.

Early Low-Grade Proteinuria: Causes, Short-Term Evolution and Long-Term Consequences in Renal Transplantation

Proteinuria 1 year after transplantation is associated with poor renal outcome. It is unclear whether low‐grade (<1 g/24 h) proteinuria earlier after transplantation and its short‐term change affect long‐term graft survival. The effects of proteinuria and its change on long‐term graft survival were retrospectively assessed in 484 renal transplant recipients. One‐ and 3‐month proteinuria correlated with donor age, donor cardiovascular death, prolonged cold and warm ischemia times and acute rejection. One‐ and 3‐month proteinuria (per 0.1 g/24 h, hazard ratio (HR): 1.07 and 1.15, p < 0.0001)—especially low‐grade proteinuria (HR: 1.20 and 1.26, p < 0.0001)—were powerful, independent predictors of graft loss. Its short‐term reduction correlated with arterial pressure (AP) (the lower the 3‐month diastolic and 12‐month systolic AP, the lower the risk of increasing proteinuria during 1–3 months and 3–12 months periods, respectively: Odds ratio (OR) per 10 MmHg: 0.78, p = 0.01 and 0.85, respectively, p = 0.02), and was associated with decreased long‐term graft loss (per 0.1 g/24 h: HR: 0.88 and 0.98, respectively, p < 0.0001), independently of initial proteinuria. Early low‐grade proteinuria due to pre‐transplant renal lesions, ischemia‐reperfusion and immunologic injuries is a potent predictor of graft loss. Short‐term reduction in proteinuria is associated with improved long‐term graft survival.

The risk of hypertension in men: direct and indirect effects of chronic smoking.

Objectives To assess the risk of hypertension associated with smoking status. Design A population-based cross-sectional study in 12 417 men screened for a routine medical and biological check-up provided by their medical insurance at the ‘Institut inter-Régional pour la Santé’ (IRSA, Regional Institute for Health), a group of 10 medical centres in Western and Central France. Main outcome measures The prevalence and the relative risk of hypertension associated with smoking status. Results Overall, the prevalence of hypertension was higher in former smokers than in never smokers (13.5 versus 8.8%, P < 0.001). The risk of hypertension was higher [odds ratio (OR) 1.31 (1.13–1.52), P < 0.001] in former smokers than in never smokers, independently of age and alcohol intake. Both current and former smokers were at risk for systolic hypertension, especially those subjects aged 60 years and above. The risk of hypertension was associated with the number of cigarettes smoked [OR per 10 cigarettes smoked daily: 1.13 (1.05–1.21), P < 0.001] and the duration of smoking cessation [OR 0.99 (0.98–1.00), P = 0.01]. When body mass index was entered into the model, the risk of hypertension in former smokers was no longer significant; however, current smokers remained at risk for systolic hypertension. Conclusions Former smokers are at risk for hypertension, probably because of the higher prevalence of overweight and obese subjects in this group. Current smokers are also at risk for systolic hypertension, especially in those subjects aged 60 years or older. However, this risk is independent of body mass index.

Reversed polarized delivery of an aquaporin-2 mutant causes dominant nephrogenic diabetes insipidus

Vasopressin regulates body water conservation by redistributing aquaporin-2 (AQP2) water channels from intracellular vesicles to the apical surface of renal collecting ducts, resulting in water reabsorption from urine. Mutations in AQP2 cause autosomal nephrogenic diabetes insipidus (NDI), a disease characterized by the inability to concentrate urine. Here, we report a frame-shift mutation in AQP2 causing dominant NDI. This AQP2 mutant is a functional water channel when expressed in Xenopus oocytes. However, expressed in polarized renal cells, it is misrouted to the basolateral instead of apical plasma membrane. Additionally, this mutant forms heterotetramers with wild-type AQP2 and redirects this complex to the basolateral surface. The frame shift induces a change in the COOH terminus of AQP2, creating both a leucine- and a tyrosine-based motif, which cause the reversed sorting of AQP2. Our data reveal a novel cellular phenotype in dominant NDI and show that dominance of basolateral sorting motifs in a mutant subunit can be the molecular basis for disease.

Genetic Investigation of Autosomal Recessive Distal Renal Tubular Acidosis: Evidence for Early Sensorineural Hearing Loss Associated with Mutations in the ATP6V0A4 Gene

Mutations in the ATP6V1B1 and ATP6V0A4 genes, encoding subunits B1 and 4 of apical H(+) ATPase, cause recessive forms of distal renal tubular acidosis (dRTA). ATP6V1B mutations have been associated with early sensorineural hearing loss (SNHL), whereas ATP6V0A4 mutations are classically associated with either late-onset SNHL or normal hearing. The phenotype and genotype of 39 new kindreds with recessive dRTA, 18 of whom were consanguineous, were assessed. Novel and known loss-of-function mutations were identified in 31 kindreds. Fourteen new and five recurrent mutations of the ATP6V0A4 gene were identified in 21 families. For the ATP6V1B1 gene, two new and two previously described mutations were identified in 10 families. Surprisingly, seven probands with ATP6V0A4 gene mutations developed severe early SNHL between the ages of 2 mo and 10 yr. No mutation was detected in eight families. These data extend the spectrum of disease-causing mutations and provide evidence for genetic heterogeneity in SNHL. The data also demonstrate that mutations in either of these genes may cause early deafness, and they highlight the importance of genetic screening for recessive forms of dRTA independent of hearing status.

Spectrum of mutations in Gitelman syndrome

Gitelmans syndrome (GS) is a rare, autosomal recessive, salt-losing tubulopathy caused by mutations in the SLC12A3 gene, which encodes the thiazide-sensitive NaCl cotransporter (NCC). Because 18 to 40% of suspected GS patients carry only one SLC12A3 mutant allele, large genomic rearrangements may account for unidentified mutations. Here, we directly sequenced genomic DNA from a large cohort of 448 unrelated patients suspected of having GS. We found 172 distinct mutations, of which 100 were unreported previously. In 315 patients (70%), we identified two mutations; in 81 patients (18%), we identified one; and in 52 patients (12%), we did not detect a mutation. In 88 patients, we performed a search for large rearrangements by multiplex ligation-dependent probe amplification (MLPA) and found nine deletions and two duplications in 24 of the 51 heterozygous patients. A second technique confirmed each rearrangement. Based on the breakpoints of seven deletions, nonallelic homologous recombination by Alu sequences and nonhomologous end-joining probably favor these intragenic deletions. In summary, missense mutations account for approximately 59% of the mutations in Gitelmans syndrome, and there is a predisposition to large rearrangements (6% of our cases) caused by the presence of repeated sequences within the SLC12A3 gene.

Urinary albumin excretion and the risk of graft loss and death in proteinuric and non-proteinuric renal transplant recipients

Background: Microalbuminuria and macroalbuminuria constitute risk factors for ESRD and death in non‐transplanted populations. Whether microalbuminuria (especially in non‐proteinuric patients) and macroalbuminuria constitute risk factors for graft loss and death is presently unknown in renal transplantation.