Mutations in a new member of the chromodomain gene family cause CHARGE syndrome.

CHARGE syndrome is a common cause of congenital anomalies affecting several tissues in a nonrandom fashion. We report a 2.3-Mb de novo overlapping microdeletion on chromosome 8q12 identified by array comparative genomic hybridization in two individuals with CHARGE syndrome. Sequence analysis of genes located in this region detected mutations in the gene CHD7 in 10 of 17 individuals with CHARGE syndrome without microdeletions, accounting for the disease in most affected individuals.

Functional expression of mutations in the human NaCl cotransporter: evidence for impaired routing mechanisms in Gitelman's syndrome.

Gitelman's syndrome is an autosomal recessive renal tubular disorder characterized by hypokalemic metabolic alkalosis, hypomagnesemia, and hypocalciuria. This disorder results from mutations in the thiazide-sensitive NaCl cotransporter (NCC). To elucidate the functional implications of mutations associated with this disorder, metolazone-sensitive (22)Na(+) uptake, subcellular localization, and glycosidase-sensitive glycosylation of human NCC (hNCC) were determined in Xenopus laevis oocytes expressing FLAG-tagged wild-type or mutant hNCC. Injection of 10 ng of FLAG-tagged hNCC cRNA resulted in metolazone-sensitive (22)Na(+) uptake of 3.4 +/- 0.2 nmol Na(+)/oocyte per 2 h. Immunocytochemical analysis revealed sharp immunopositive staining at the plasma membrane. In agreement with this finding, a broad endoglycosidase H-insensitive band of 130 to 140 kD was present in Western blots of total membranes. The plasma membrane localization of this complex-glycosylated protein was confirmed by immunoblotting of purified plasma membranes. The mutants could be divided into two distinct classes. Class I mutants (G439S, T649R, and G741R) exhibited no significant metolazone-sensitive (22)Na(+) uptake. Immunopositive staining was present in a diffuse band just below the plasma membrane. This endoplasmic reticulum and/or pre-Golgi complex localization was further suggested by the complete absence of the endoglycosidase H-insensitive band. Class II mutants (L215P, F536L, R955Q, G980R, and C985Y) demonstrated significant metolazone-sensitive (22)Na(+) uptake, although uptake was significantly lower than that obtained with wild-type hNCC. The latter mutants could be detected at and below the oocyte plasma membrane, and immunoblotting revealed the characteristic complex-glycosylated bands. In conclusion, this study substantiates NCC processing defects as the underlying pathogenic mechanism in Gitelman's syndrome.

Exclusion of mutations in FXYD2, CLDN16 and SLC12A3 in two families with primary renal Mg2+ loss.

BACKGROUND: Based on genetic studies in families with hereditary renal Mg(2+) reabsorption disorders, several genes were shown to be involved in renal Mg(2+) transport. Mutations in the CLDN16 gene were found to underlie autosomal recessive hypomagnesaemia associated with hypercalciuria and nephrocalcinosis. The FXYD2 gene was implicated in autosomal dominant renal Mg(2+) wasting associated with hypocalciuria. Mutations in the SLC12A3 gene, also known as NCC, cause Gitelman's syndrome. In addition to hypokalaemic metabolic alkalosis, hypomagnesaemia associated with hypocalciuria is considered to be a hallmark feature of this latter disorder. METHODS: We have characterized a new family with presumed dominant renal hypomagnesaemia by detailed clinical examination and mutation analysis of CLDN16, FXYD2 and SLC12A3. In addition, we have performed mutation analysis of these three genes in a previously described family with autosomal recessive renal Mg(2+) wasting. In this family, linkage analysis was performed with polymorphic markers in the vicinity of the FXYD2 gene. RESULTS: The phenotype of the new family closely resembles that of the known dominant families with a mutation in FXYD2, but mutations in this gene were not identified in the new family. No mutations were found in CLDN16 and SLC12A3 either. Sequencing of the three genes in the patients of the recessive family revealed no mutations. In addition, haplotype analysis excluded linkage to the FXYD2 region on chromosome 11q23. CONCLUSION: Our results indicate that, in addition to the currently known loci involved in renal Mg(2+) handling, at least one other gene must be involved.