Genetic Analysis Of Non-syndromic Hearing Loss And Waardenburg Syndrome

Hearing impairment is most common sensory function disorder, and influence human life quality. Genetic factors play more important role in the etiology of hearing impairment for environmental factors are controlled gradually and effectively. The mechanism of hearing function and hearing losss have been eclucidated benefiting from Molecular Genetic research and some of results have been applied in clinical molecular diagnosis for deafness. In order to explore the mechanism of genetic hearing loss and supply clinic practice with more high-quality service, our research focuses on the genetic analysis of autosomal-dominant non-syndromic hearing loss, mitochondrial mutation induced hearing loss and Waardenburg syndrome through clinical characteristic evaluation and molecular defect identification.PART 1: Clinic characteristic and mapping and identification of pathogenic gene in three late-onset sensorineural hearing loss pedigrees1. Autosomal-dominant non-syndromic hearing loss Family HB-C034 is characteristic of mid-frequency hearing loss. Critical interval of 12 cM was determined between markers D6S407 and D6S1009 by linkage analysis, which overlaps DFNA10 locus. Two-point LOD score was 4.51 atθ=0.00. Sequencing of candidate gene EYA4 revealed a missense mutation c.1615A>G in exon 17, causing amino acid substitution arginine to glycine at a conservative position 539. The mutation is consistent with hearing loss in family HB-C034 and has not been found in 50 random controls. So far, this is first EYA4 missense mutation in DFNA10 families. Further analysis and work are needed for the significance of the mutation.2. Autosomal-dominant non-syndromic hearing loss Family DX-J033 presents late-onset hearing loss, ages of onset are between 20 to 47 years old, and high-frequency is involved firstly. Genomewide linkage analysis revealed significant linkage of markers D11S911,D11S937,D11S4166,D11S901 with the disease phenotype. By haplotype analysis, a linkage region contains the candidate gene MY07A. Six mutations were found by MY07A sequencing. c.652G>A and c.2732G>A are not SNPs and cosegregate with the phonotype. c.652 G>A (D218N) in exon7 is located in a conservative site and has not been found in 50 random controls. c.2732G>A (R911Q) in exon23 is located in a conservative site. To verify the significance of these missense mutations are needed.3. Autosomal-dominant non-syndromic hearing loss Family DX-J033 displays low-frequency sensorineural hearing loss and ages of onset are between 10 to 20 years old. The candidate locus DFNA1,DFNA6/14/38 and DFNA54 , which involve in low-frequency hearing loss, has been precluded by linkage analysis. The novel deafness related gene is expected to be found by the following genomewide linkage analysis.PART 2: Molecular epidemiology investigation on mitochondrial tRNA-Ser^UCN gene mutation and mitochondrial DNA mutation analysis in a maternally transmitted hereditary sensorineural hearing loss pedigree1. Molecular epidemiology investigation aiming to mitochondrial DNA 7444,7445 point mutations screen revealed fourteen carrier in 3414 hearing loss samples, of which twelve with G7444A, one with A7445T, and one with A7445C, positive detection rate was 4.1‰. A novel mutation style, coexistence of C1494T mutation of 12SrRNA gene and G7444A mutation of tRNA-Ser^UCN gene was found in two patients, synergistic effect of the two mutations was not clear at present. Two 7445 point mutation carriers were sporadic cases with very low penetrance, suggesting the mutation alone were not enough to cause deafness and environment factors or nuclear gene worked together.2. Family MZ569 is a maternally transmitted hereditary sensorineural hearing loss pedigree, in which six of seventeen maternal members suffered different level of hearing loss. Coexistence of A1555 and 961delT+insC mutations in mitochondrial 12S rRNA gene was screened and presumed to work together in the development of deafness.PART 3: Clinical characteristic evaluation and pathogenic gene mutation analysis for Waardenburg Syndrome1. Clinical characteristic evaluation and MITF mutations screening in twelve cases with WS2 revealed four novel mutations. Mutations c.639delA and c.368delT cause premature stop codon and truncating protein: p.I220X and p.L126X separately. Deletion mutation c.635-9₆35-5delTTCTT, which locates near 5' splice site of exon 7, was thought to affect normal splicing and causing MITF functional disturbance. Missense mutation c.638A>G causes amino acid substitution from glumatic acid to glycine. These novel mutations enrich Chinese MITF mutation spectrum in WS2 cases, and provide evidence in the following gene diagnosis.2. Clinical characteristic evaluation and PAX3 mutations screening in three cases with WS1 revealed two novel mutations. Heterozygous mutation c.792+1G>A in intron 5 splice site was supposed to affect normal splicing and causing PAX3 functional impairment. And a WS2 pedigree carrying c.241G>C mutation (p.G81R) displays phenotype variance between members, confirming diverse penetrance in every WS1 case.