Simultaneous sequencing of 37 genes identified causative mutations in the majority of children with renal tubulopathies.

The clinical diagnosis of inherited renal tubulopathies can be challenging as they are rare and characterized by significant phenotypic variability. Advances in sequencing technologies facilitate the establishment of a molecular diagnosis. Therefore, we determined the diagnostic yield of a next generation sequencing panel assessing relevant disease genes in children followed through three national networks with a clinical diagnosis of a renal tubulopathy. DNA was amplified with a kit provided by the European Consortium for High-Throughput Research in Rare Kidney Diseases with nine multiplex PCR reactions. This kit produced 571 amplicons covering 37 genes associated with tubulopathies followed by massive parallel sequencing and bioinformatic interpretation. Identified mutations were confirmed by Sanger sequencing. Overall, 384 index patients and 16 siblings were assessed. Most common clinical diagnoses were 174 patients with Bartter/Gitelman syndrome and 76 with distal renal tubular acidosis. A total of 269 different variants were identified in 27 genes, of which 95 variants were considered likely, 136 definitely pathogenic and 100 had not been described at annotation. These mutations established a genetic diagnosis in 245 of the index patients. Genetic testing changed the clinical diagnosis in 16 cases and provided insights into the phenotypic spectrum of the respective disorders. Our results demonstrate a high diagnostic yield of genetic testing in children with a clinical diagnosis of a renal tubulopathy, consistent with a predominantly genetic etiology in known disease genes. Thus, genetic testing helped establish a definitive diagnosis in almost two-thirds of patients thereby informing prognosis, management and genetic counseling.

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.

Prevalence of Novel MAGED2 Mutations in Antenatal Bartter Syndrome.

BACKGROUND AND OBJECTIVES: Mutations in the MAGED2 gene, located on the X chromosome, have been recently detected in males with a transient form of antenatal Bartter syndrome or with idiopathic polyhydramnios. The aim of this study is to analyze the proportion of the population with mutations in this gene in a French cohort of patients with antenatal Bartter syndrome. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: The French cohort of patients with antenatal Bartter syndrome encompasses 171 families. Mutations in genes responsible for types 1-4 have been detected in 75% of cases. In patients without identified genetic cause (n=42), transient antenatal Bartter syndrome was reported in 12 cases. We analyzed the MAGED2 gene in the entire cohort of negative cases by Sanger sequencing and retrospectively collected clinical data regarding pregnancy as well as the postnatal outcome for positive cases. RESULTS: We detected mutations in MAGED2 in 17 patients, including the 12 with transient antenatal Bartter syndrome, from 16 families. Fifteen different mutations were detected (one whole deletion, three frameshift, three splicing, three nonsense, two inframe deletions, and three missense); 13 of these mutations had not been previously described. Interestingly, two patients are females; in one of these patients our data are consistent with selective inactivation of chromosome X explaining the severity. The phenotypic presentation in our patients was variable and less severe than that of the originally described cases. CONCLUSIONS: MAGED2 mutations explained 9% of cases of antenatal Bartter syndrome in a French cohort, and accounted for 38% of patients without other characterized mutations and for 44% of male probands of negative cases. Our study confirmed previously published data and showed that females can be affected. As a result, this gene must be included in the screening of the most severe clinical form of Bartter syndrome.

Isocitrate dehydrogenase mutations are rare in pheochromocytomas and paragangliomas.

CONTEXT: Paragangliomas and pheochromocytomas are neuroendocrine tumors that occur sporadically and in the context of inherited tumor syndromes including hereditary paraganglioma-pheochromocytoma syndrome and von Hippel-Lindau disease (VHL). The paraganglioma-pheochromocytoma syndrome is caused by germline-inactivating mutations in the mitochondrial succinate dehydrogenase (SDH) genes SDHB, SDHC, SDHD, or SDHAF2, and VHL is the result of inactivating VHL gene mutations. In SDH- and VHL-related paraganglioma and pheochromocytoma, hypoxia-inducible factor (HIF) stabilization has been described as the causal oncogenic event. Recently, HIF activation has also been found in glioblastoma multiforme, as the result of somatic mutational inactivation of the isocitrate dehydrogenase (IDH) type 1 or type 2 enzymes. These findings suggest that inactivating IDH1 and IDH2 mutations might also play a role in paraganglioma and pheochromocytoma tumorigenesis, especially in non-SDH- or non-VHL-related tumors. DESIGN: We investigated 365 pheochromocytomas and paragangliomas, including 269 sporadic tumors without SDH or VHL gene mutations, for mutations in IDH1 and IDH2. Only codons 132 and 172 were screened because these are the ones exclusively involved. RESULTS: In one of 131 paragangliomas, a somatic heterozygous IDH1 p.Arg132Cys mutation was detected in a sporadic carotid paraganglioma diagnosed in a 61-yr-old woman. No mutations were found in 234 pheochromocytomas. CONCLUSION: IDH mutations are very rare in paragangliomas and pheochromocytomas and do not appear to play an important role in oncogenic HIF activation known to be present in these tumors.

Report of a family with two different hereditary diseases leading to early nephrocalcinosis.

The etiologies of early onset nephrocalcinosis in consanguineous families include five major inherited recessive disorders: primary hyperoxaluria (PH), familial hypomagnesemia with hypercalciuria and nephrocalcinosis (FHHNC), distal renal tubular acidosis (dRTA), hereditary hypophosphatemic rickets with hypercalciuria (HHRH) and antenatal Bartter syndrome. In this paper, we describe two girls from consanguineous parents with early onset nephrocalcinosis. Based on both clinical and biochemical assessment in combination with molecular genetics, we have shown that the etiology of nephrocalcinosis is different in each girl: one had FHHNC and her sister had dRTA.