Study Of Molecular Mechanism Of Non-syndromic Hereditary Hearing Loss

Hearing impairment is the most common birth defect and sensorineural disorder. Based on the national survey of disabled population in 2006, the total number of hearing impairment in China was 27.8 millions. And the number of newborn with congenital hearing impairment reaches to 20-30 thousands every year. Genetic factors play more important role in the etiology of hearing impairment for the environmental factors are controlled gradually and effectively. To improve the prevention and treatment of hearing impairment and to reduce the number of cases with hearing loss, it is necessary to conduct the study on the cause and molecular mechanism of hearing impairment. In this study, we focus on the molecular cause and mechanism of the hereditary non-syndromic hearing impairment. The study divided into three parts according to three families.PART1:The confirmation of the causative gene PRPS1 of DFN2 and the functional study of all mutants.In the previous study of our research group, we found that the candidate gene of GZ-Z052 family with X-linked non-syndromic hearing impairment is PRPS1, with mutation of c.193G>A(p.D65N). The locus (Xq22) of the gene overlapped to that of three previously reported DFN2 families. Mutation screening of PRPS1 gene was carried out in the three DFN2 families and different missense mutation in PRPS1 gene was identified in each family. The mutations are c.259G>A (p.A87T), c.869T>C(p.1290T)and c.916G>A(p.G306R), faithfully segregating with the hearing loss in each family. None of the four mutations were seen in 1025 unrelated control chromosomes, supporting the pathogenicity of the mutations.The activity of the PRPS of erythrocyte and cultured fibroblast of the affected males of GZ-Z052 family were 56% and 55% of the normal controls. The activity of all of six mutants of PRPS 1 (p.D65N, p.A87T, p.I290T, p.G306R, p.M115T, and p.Q133P) expressed in E. coli BL21, were decreased. The enzyme activity of the four mutants were between that of wild type and p.M115T and p.Q133P, indicating that DFN2 is caused by mutation of PRPS1 gene.PART 2:Identification of causative gene of SX-Z089 family and prenatal diagnosis conducted in this familySX-Z089 family exhibits X-linked non-syndromic hearing impairment. The affected males had typical temporal bone CT imaging of DFN3, e.g, bilateral dilation of the internal auditory canals and with a fistulous communication between its lateral aspect and the basal turn of the cochlea. A c.647G>A (p.G216E) mutation in POU3F4 gene was found segregating with the phenotype of the family. The G216 is conserved from clawed frog to human. The mutation was absent in 110 normal controls. A hemizygotic mutation of c.647G>A in POU3F4 gene was found in the DNA sample of the amniotic fluid in prenatal diagnosis, indicating that the fetus will copy the phenotype of the affected males of the family.Nine maternal members of SX-Z089 family carried mtDNA 961delT/insC(n) mutation. This mutation do not segregate with the phenotype of the family. The mtDNA 961delT/insC(n) mutation is unlikely the causative mutation of the family. The mtDNA 961delT/insC(n) had been reported to associate with the aminoglycoside-induced hearing loss. However, in SX-Z089 family some members with mtDNA 961delT/insC(n) mutation did not have hearing loss even had a history of aminoglycoside use. The role of mtDNA 961delT/insC(n) in aminoglycoside-induced hearing loss remains to be confirmed.PART 3:Gene mapping of HN-J069 family with autosomal dominant hereditary non-syndromic hearing impairmentWe have collected a family with autosomal dominant non-syndromic hereditary hearing loss (DFNA) from HeNan province. Twenty-two DFNA loci with known genes had been ruled out by linkage analysis using the STR markers near the known DFNA genes in family HN-J069. We have mapped the disease locus to 30cM interval on chromosome 5, between 5q33.3 and 5q35.3, by genome wide SNP typing. Fine mapping will be conducted with STR markers in this interval. This will lead to identification of a new deafness gene in this family.