IVS8+1 DelG, a Novel Splice Site Mutation Causing DFNA5 Deafness in a Chinese Family / 中华医学杂志(英文版)

<p><b>BACKGROUND</b>Nonsyndromic hearing loss (NSHL) is highly heterogeneous, in which more than 90 causative genes have currently been identified. DFNA5 is one of the deafness genes that known to cause autosomal dominant NSHL. Until date, only five DFNA5 mutations have been described in eight families worldwide. In this study, we reported the identification of a novel pathogenic mutation causing DFNA5 deafness in a five-generation Chinese family.</p><p><b>METHODS</b>After detailed clinical evaluations of this family, the genomic DNA of three affected individuals was selected for targeted exome sequencing of 101 known deafness genes, as well as mitochondrial DNA and microRNA regions. Co-segregation analysis between the hearing loss and the candidate variant was confirmed in available family members by direct polymerase chain reaction (PCR)-Sanger sequencing. Real-time PCR (RT-PCR) was performed to investigate the potential effect of the pathogenic mutation on messenger RNA splicing.</p><p><b>RESULTS</b>Clinical evaluations revealed a similar deafness phenotype in this family to that of previously reported DFNA5 families with autosomal dominant, late-onset hearing loss. Molecular analysis identified a novel splice site mutation in DFNA5 intron 8 (IVS8+1 delG). The mutation segregated with the hearing loss of the family and was absent in 120 unrelated control DNA samples of Chinese origin. RT-PCR showed skipping of exon 8 in the mutant transcript.</p><p><b>CONCLUSIONS</b>We identified a novel DFNA5 mutation IVS8+1 delG in a Chinese family which led to skipping of exon 8. This is the sixth DFNA5 mutation relates to hearing loss and the second one in DFNA5 intron 8. Our findings provide further support to the hypothesis that the DFNA5-associated hearing loss represents a mechanism of gain-of-function.</p>

Nonsyndromic inherited hearing impairment caused by mtDNA double mutations of A1555G and 961 insC / 中华医学遗传学杂志

<p><b>OBJECTIVE</b>To investigate the genotypes of mitochondrial DNA mutations of a large nonsyndromic inherited hearing impairment pedigree.</p><p><b>METHODS</b>The diagnosis was validated by hearing test. Blood samples from the branch pedigree (33 members) and 6 sporadic patients were obtained. DNA was extracted from the leukocytes. The mitochondrial DNA target fragments were amplified by polymerase chain reaction(PCR). The 1555G, 3243G and 7445G mutations were detected by BsmA I, Apa I and Xba I restriction endonuclease digestion respectively. Some PCR products were analyzed by sequencing.</p><p><b>RESULTS</b>Restriction endonuclease digestion identified that 17 patients from the pedigree carried 1555G mutation. All pedigree members, including patients and sporadic patients, did not have 3243G and 7445G mutation. In 6 patients of the pedigree DNA sequence analysis revealed double mutations, an A>G transition at position 1555 and a C insertion at position 961, whereas the unaffected relatives of the pedigree and sporadic patients did not have such mutations. None of them carried 3243G and 7445G mutation.</p><p><b>CONCLUSION</b>Double mutations of A1555G and 961 insC in mitochondrial DNA 12S rRNA gene region may play a pivotal role in the pathogenesis of hearing loss in the large nonsyndromic inherited hearing impairment pedigree.</p>