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 Correspondence should be addressed to F.H. (fhilde@umich.edu). 12 These authors contributed equally to this work 13 These authors contributed equally to this work GenBank accession numbers. INVS cDNA, NM_014425; Invs cDNA, NM_010569; invs cDNA, AF465261; INVS in chromosome 9 genome contig, NT_008470.URLs. Additional information is available at http://danio.mgh.harvard.edu/blast/blast.html. Note: Supplementary information is available on the Nature Genetics website. Competing Interests Statement:The authors declare that they have no competing financial interests. NIH Public AccessAuthor Manuscript Nat Genet. Author manuscript; available in PMC 2013 August 02. NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript 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 leftright axis determination.NPHP, an autosomal recessive cystic kidney disease, is the most frequent genetic cause for end-stage renal failure in children and young adults [1][2][3] . Causative mutations in two genes (NPHP1 and NPHP4) have been identified by positional cloning [4][5][6][7] . There is considerable interest in identifying genes associated with NPHP because its most prominent feature is development of renal interstitial fibrosis 8 , which in chronic renal disease of all origin represents the pathogenic event correlated most strongly to loss of renal function 9 . As little was known about the pathogenesis of NPHP, positional cloning was used to identify a new gene, NPHP1, mutations in which cause NPHP1 (OMIM 256100; refs. 4,5). It encodes a novel docking protein, nephrocystin [10][11][12][13] , that interacts with components of cell-cell and cell-matrix signaling, such as focal adhesion kinase 2, tensin, p130Cas and filamin, and with nephrocystin-4 or nephroretinin, the product of NPHP4, mutations in which cause NPHP4 (OMIM 606966; refs. 6,7). Identification of the genes NPHP1 and NPHP4, which are conserved in evolution including in the nematode Caenorhabditis elegans, offered new insights into mechanisms of cell-cell and cell-matrix signaling...

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 CFHϩIF mutations). Age Ͻ3 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 Ͻ1 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.

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.

Several studies have demonstrated genetic predisposition in non-shigatoxin-associated hemolytic uremic syndrome (HUS), involving regulatory proteins of the complement alternative pathway: Factor H (FH) and membrane co-factor protein (CD46). Regarding the observations of thrombotic thrombocytopenic purpura patients, in whom a von Willebrand factor protease (ADAMST-13) deficiency may be inherited or acquired secondary to IgG antibodies, it was speculated that HUS might occur in a context of an autoimmune disease with the development of anti-FH antibodies leading to an acquired FH deficiency. The presence of FH autoantibodies was investigated by an ELISA method using coated purified human FH in a series of 48 children who presented with atypical HUS and were recruited from French university hospitals. Anti-FH IgG antibodies were detected in the plasma of three children who presented with recurrent HUS. The anti-FH specificity was conserved by the Fab2 fraction. The plasma FH activity was found to be decreased, whereas plasma FH antigenic levels and FH gene analysis were normal, indicating that the presence of anti-FH antibodies led to an acquired functional FH deficiency. This report supports for the first time that HUS may occur in a context of an autoimmune disease with the development of anti-FHspecific antibody leading to an acquired FH deficiency. This new mechanism of functional FH deficiency may lead to the design of new approaches of diagnosis and treatment with a particular interest in plasma exchanges or immunosuppressive therapies.

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 dem- IntroductionMutations in the genes encoding the complement regulators factor H, 1-6 factor I, 7,8 and membrane cofactor protein (MCP; CD46), 9,10 as well as in the activating component factor B, 11 have been detected in approximately 50% of patients with atypical hemolytic uremic syndrome (aHUS). 12 A proportion of the remaining patients have persistently low serum levels of C3. In this study we have examined the hypothesis that mutations in the gene encoding C3 could be associated with aHUS in these patients.C3 is the pivotal component of the complement system. 13 Activation of the classical, lectin, and alternative pathways results in cleavage of C3 to generate C3b and the anaphylatoxin C3a. When C3b is produced, the thioester is cleaved, and then this highly reactive species may bind covalently to targets. Interaction of the zymogen factor B with C3b and subsequent cleavage of factor B by factor D results in formation of the alternative pathway C3 convertase C3bBb. This set of reactions represents an amplification loop.A series of complement regulators including factor H and MCP prevent feedback via this loop by increasing the rate of dissociation of C3bBb and/or by serving as cofactors for the serine protease factor I to cleave C3b. Mutations in the gene encoding factor B were recently found to enhance formation of C3bBb or increase resistance to inactivation. 11 The importance of C3 as a susceptibility factor for human disease has been emphasized by recent studies documenting that a common nonsynonymous coding change in C3 (rs2230199, Arg80Gly, corresponding to C3S and C3F) is both a susceptibility factor for age-related macular degeneration 14 and associated with long-term renal allograft survival. 15 Methods SubjectsIn 2 independent cohorts of aHUS patients (Paris, France and Newcastle upon Tyne, United Kingdom), 26 patients (17 Paris, 9 Newcastle) with a serum C3 level persistently below the lower end of the normal range of 680 to 1380 mg/L were identified. In these patients functionally significant mutations in CFH, MCP, CFI, and CFB had not previously been detected. Mutation screening of C3 was undertaken in these patients.Approval for this study was obtained from the Departement de la Rechereche Clinique et du Developement, DRRC Ile de France, France and the Northern and Mutation screeningThe coding sequence of C3 was amplified with flanking primers (Table S1, available on the Blood website; see the Supplemental Materials link at the top of the online article). Direct sequencing was undertaken using a 96-capillary Sequencer 3700 (Applied Biosyst...

Several case reports suggest that rituximab (RTX) could be effective in steroid-dependent nephrotic syndrome, but RTX efficacy has not yet been studied in a series of patients. Safety and efficacy of RTX were assessed in a multicenter series of 22 patients aged 6.3-22 years with severe steroid-dependent nephrotic syndrome or steroid-resistant but cyclosporin-sensitive idiopathic nephrotic syndrome. Patients were treated with two to four infusions of RTX. Seven patients were nephrotic at the time of RTX treatment. Peripheral B cells were depleted in all subjects. Remission was induced in three of the seven proteinuric patients. One or more immunosuppressive (IS) treatments could be withdrawn in 19 patients (85%), with no relapse of proteinuria and without increasing other IS drugs. RTX was effective in all patients when administered during a proteinuria-free period in association with other IS agents. When relapses occurred, they were always associated with an increase in CD19 cell count. Adverse effects were observed in 45% of cases, but most of them were mild and transient. This study suggests that RTX could be an effective treatment for severe steroid-dependent nephrotic syndrome.

Gitelman's 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 ligationdependent 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 Gitelman's syndrome, and there is a predisposition to large rearrangements (6% of our cases) caused by the presence of repeated sequences within the SLC12A3 gene.

Joubert syndrome (JS) is an autosomal recessive disorder that is described in patients with cerebellar ataxia, mental retardation, hypotonia, and neonatal respiratory dysregulation. Kidney involvement (nephronophthisis or cystic renal dysplasia) is associated with JS in one fourth of known cases. Mutations in three genes-AHI1, NPHP1, and NPHP6-have been identified in patients with JS. However, because NPHP1 mutations usually cause isolated nephronophthisis, the factors that predispose to the development of neurologic involvement are poorly understood. In an attempt to identify such genetic determinants, a cohort of 28 families with nephronophthisis and at least one JS-related neurologic symptom were screened for mutations in AHI1, NPHP1, and NPHP6 genes. NPHP1 and NPHP6 homozygous or compound heterozygous mutations were found in 13 (46%) and six (21%) unrelated patients, respectively. Two of the 13 patients with NPHP1 mutations carried either a heterozygous truncating mutation in NPHP6 or a heterozygous missense mutation in AHI1. Furthermore, five patients with NPHP1 mutations carried the AHI1 variant R830W, which was predicted to be "possibly damaging" and was found with significantly higher frequency than in healthy control subjects and in patients with NPHP1 mutations without neurologic symptoms (five of 26 versus four of 276 and three of 152 alleles; P < 0.001 and P < 0.002, respectively). In contrast to the variable neurologic and milder retinal phenotype of patients with NPHP1 mutations, patients with NPHP6 mutations presented with a more severe neurologic and retinal phenotype. In conclusion, NPHP1 and NPHP6 are major genes of nephronophthisis associated with JS. Epistatic effects that are provided by heterozygous NPHP6 and AHI1 mutations and variants may contribute to the appearance of extrarenal symptoms in patients with NPHP1 mutations.