Usher syndrome (USH) is a group of autosomal recessive sensory disorders characterized by progressive retinitis pigmentosa (RP) and sensorineural hearing impairment. Usher syndrome type 1 (USH1), with additional vestibular dysfunction, represents the most severe form and shows extensive allelic and non-allelic heterogeneity. At least six USH1 loci exist (USH1A-F), and four of the underlying genes have been identified. Recently, a novel gene, cadherin 23 (CDH23), was shown to be mutated in USH1D. We performed mutation screening by single strand conformation polymorphism (SSCP) analysis and direct sequencing on 33 USH1 patients previously excluded for USH1B and USH1C. On eight disease alleles of four patients, four different mutations were identified, three of them novel (c.6933delT, c.5712G-->A, and IVS45-9G-->A). Exon trapping experiments were performed with two mutations. In the case of a c.5712G-->A transition of the last base of exon 42, that is an apparently synonymous mutation, skipping of exon 42 was observed. By the mutation IVS45-9G-->A, a novel splice acceptor site was created and the insertion of 7 intronic bp was observed. Two mutations, IVS45-9G-->A and the previously described IVS51+5G-->A, were each found in more than one patient. Haplotype analysis by SNPs within CDH23 suggests common ancestors for each of the mutations. Among the total of 52 USH1 cases studied by us, CDH23 mutations account for about 10% of all disease alleles. Our results further suggest that in patients with a typical USH1D phenotype, a significant portion of CDH23 mutations leads to premature termination of translation or loss of numerous amino acid residues, with a high frequency of changes causing aberrant splicing of CDH23 mRNA.
"Eight pathogenic or presumably pathogenic mutations in CDH23 were found in six patients, specifically, a previously reported mutation that affects splicing (c.6050-9G>A) , a novel nucleotide deletion (c.6404_6405delAG; p.E2135fsX31), and six missense mutations [55,56], four of which (p.R1189W, p.R1379P, p.D2639G, and p.R3043W) had not been previously reported. They affect amino acid residues located in the 11th, 13th and 25th cadherin repeat and the extracellular region adjacent to the transmembrane domain (3065-3085), respectively (Tables 2, 3 Figure 1). "
[Show abstract][Hide abstract] ABSTRACT: Usher syndrome (USH) combines sensorineural deafness with blindness. It is inherited in an autosomal recessive mode. Early diagnosis is critical for adapted educational and patient management choices, and for genetic counseling. To date, nine causative genes have been identified for the three clinical subtypes (USH1, USH2 and USH3). Current diagnostic strategies make use of a genotyping microarray that is based on the previously reported mutations. The purpose of this study was to design a more accurate molecular diagnosis tool.
We sequenced the 366 coding exons and flanking regions of the nine known USH genes, in 54 USH patients (27 USH1, 21 USH2 and 6 USH3).
Biallelic mutations were detected in 39 patients (72%) and monoallelic mutations in an additional 10 patients (18.5%). In addition to biallelic mutations in one of the USH genes, presumably pathogenic mutations in another USH gene were detected in seven patients (13%), and another patient carried monoallelic mutations in three different USH genes. Notably, none of the USH3 patients carried detectable mutations in the only known USH3 gene, whereas they all carried mutations in USH2 genes. Most importantly, the currently used microarray would have detected only 30 of the 81 different mutations that we found, of which 39 (48%) were novel.
Based on these results, complete exon sequencing of the currently known USH genes stands as a definite improvement for molecular diagnosis of this disease, which is of utmost importance in the perspective of gene therapy.
"a Mutation lies within linker region between these two EC-repeat domains. b Mutations reported by either Bolz et al. (2001) or von Brederlow (2002). c Detected at either beginning or end of the exon, predicted to decrease splicing efficiency. "
[Show abstract][Hide abstract] ABSTRACT: Usher syndrome type I is characterized by congenital hearing loss, retinitis pigmentosa (RP), and variable vestibular areflexia. Usher syndrome type ID, one of seven Usher syndrome type I genetic localizations, have been mapped to a chromosomal interval that overlaps with a nonsyndromic-deafness localization, DFNB12. Mutations in CDH23, a gene that encodes a putative cell-adhesion protein with multiple cadherin-like domains, are responsible for both Usher syndrome and DFNB12 nonsyndromic deafness. Specific CDH23 mutational defects have been identified that differentiate these two phenotypes. Only missense mutations of CDH23 have been observed in families with nonsyndromic deafness, whereas nonsense, frameshift, splice-site, and missense mutations have been identified in families with Usher syndrome. In the present study, a panel of 69 probands with Usher syndrome and 38 probands with recessive nonsyndromic deafness were screened for the presence of mutations in the entire coding region of CDH23, by heteroduplex, single-strand conformation polymorphism, and direct sequence analyses. A total of 36 different CDH23 mutations were detected in 45 families; 33 of these mutations were novel, including 18 missense, 3 nonsense, 5 splicing defects, 5 microdeletions, and 2 insertions. A total of seven mutations were common to more than one family. Numerous exonic and intronic polymorphisms also were detected. Results of ophthalmologic examinations of the patients with nonsyndromic deafness have found asymptomatic RP-like manifestations, indicating that missense mutations may have a subtle effect in the retina. Furthermore, patients with mutations in CDH23 display a wide range of hearing loss and RP phenotypes, differing in severity, age at onset, type, and the presence or absence of vestibular areflexia.
The American Journal of Human Genetics 09/2002; 71(2):262-75. DOI:10.1086/341558 · 10.93 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Given the unique biological requirements of sound transduction and the selective advantage conferred upon a species capable of sensitive sound detection, it is not surprising that up to 1% of the approximately 30,000 or more human genes are necessary for hearing. There are hundreds of monogenic disorders for which hearing loss is one manifestation of a syndrome or the only disorder and therefore is nonsyndromic. Herein we review the supporting evidence for identifying over 30 genes for dominantly and recessively inherited, nonsyndromic, sensorineural deafness. The state of knowledge concerning their biological roles is discussed in the context of the controversies within an evolving understanding of the intricate molecular machinery of the inner ear.
Annual Review of Genomics and Human Genetics 02/2003; 4:341-402. DOI:10.1146/annurev.genom.4.070802.110347 · 8.96 Impact Factor
Data provided are for informational purposes only. Although carefully collected, accuracy cannot be guaranteed. The impact factor represents a rough estimation of the journal's impact factor and does not reflect the actual current impact factor. Publisher conditions are provided by RoMEO. Differing provisions from the publisher's actual policy or licence agreement may be applicable.