Mapping And Postional Cloning The Causative Genes In Chinese Pedigrees With Non-syndromic Hereditary Hearing Impairment

Hearing loss is a common sensory disorder in the human population. The incidence of congenital hearing loss is estimated at 1 in 1,000 births, of which approximately equal numbers of cases are attributed to environmental and genetic factors. Of the hearing-loss disorders attributable to genetic causes, ~70% are classified as nonsyndromic and the remaining 30% as syndromic. Among the many disorders classified as syndromic hearing loss, the pathology varies widely, but, in nonsyndromic hearing impairment, the defect is generally sensorineural. Nonsyndromic hearing impairment can be further subdivided by mode of inheritance: autosomal recessive(~70%);autosomal dominant (22%);X-linked (1%);mitochondrial inheritance( 30 genes for syndromic hearing loss (include AlporU BOR> Waardenburg syndrome ,some genes cause multiple forms of hearing impairment). Identifying these genes and characterizing their function will increase our knowledge of the molecular processes involved in the auditory system and will improve our understanding of how such processes can become altered and lead to hearing impairment.In our research, we used the plenty genetic resourses established in the Otolaryngology Institute of PLA general hospital to hunt for causative genes in one Chinese pedigree with congenital conductive hearing impairment and ptosis as two large Chinese pedigrees with non-syndromic hearing loss.By using the family tree,high-dense genetic markers,linkage analysis and ststistic genetics,we first successfully mapped the gene locus for this conductive hearing impairment on 12pl2.3-13.2(family 028),named DFNC1 (admitted by Committee of Human Gene Nomenclature) , and screened some candidate genes in this field. In our study ,we also mapped the two pedigrees with non-syndromic hearing losss on 9P13.2-13.3 (family 686 ,DFNA55) and llq 13.4-22.1 (family Z029).In order to present the result for this study,we divived this thesis into two parts as below:PART 1: Mapping and cloning the causative genes in Chinese pedigree with congenital conductive hearing impairment and ptosisIn our study, we luckily found a large Chinese family with autosomal dominant inheritance pattern of congenital conductive hearing impairment andptosis,named family 028.We investigated 44 individuals in the pedigree and found a sequence of the conductive hearing impairment transmitted through four generations. The genetic forms of hearing loss in 19 members of the 028 pedigree were diagnosed by otologic, audiologic, and physical examination, family history, ancillary testing (CT examination of the temporal bone). 9 individuals of 19 were diagnosed congenital condutive hearing impairment and bilateral ptosis, 1 has only symptom of ptosis. Tympanotomy in two patients with conductive hearing impairment showed such hearing loss was derived from malformations of middle ear(malformation of ossicular chain and stape fixation). Genome scan and linkage analysis was carried out on 028 pedigree and mapped the gene to 12pl2.3-13.2. This resulted in significant evidence for linkage to the markers D12S308 (two-point lod-score of 3.45 at theta=0.0) and a candidate critical region of 12.01cM between markers D12S1697 and D12S310. No known hearing impairment genes or loci are localized within this region , so We first named this gene locus for hereditary conductive hearing impairment as DFNC1 (conductive deafness,autosomal,locus l),and was approved by the Committee of Human Gene Nomenclature. According to the physiopathological mechanism and embryology of middle ear, we screened some candidate genes in DFNC1 gene locus,such as SOX5, MGP and DULP16.The results exclude these genes and reduce the candidate range of causative genes.In order to investigate the clinical classification and relationship with conductive hearing impairment of congenital middle ear malformations,we selected 64 patients(82 ears) with single congenital middle ear malformations who had been operated in the ENT Department of the PLA General Hospital from 1995 to 2004. According to the embryologic development of the structures in middle ear,congenital middle ear malformations were classified 4 types.Type Axongenital ossicular chain anomaliesjtype Bxongenital fusion of stapes;type Cxongenital hypoplasia or atresia of oval/round widows.Hearing loss of three types on language frequency have no obvious diference(p=0.1617),but there were statistical diference on high frequency(>2kHz) between type A with type B andtype C (p<0.05) . Furthermore,descension of bone conduction and mixed hearing impairment were familiar in type B and C. According to the results,we draw the conclusion that it was reational that congenital middle ear malformations were classied 3 types found on the embryologic development.Hearing loss due to middle ear malformations could be distinguished by descension of bone conduction and air conducion on high frequency(>2kHz).PART 2: Mapping the relevant Loci in the families with non-syndromic hereditary hearing impairment on Chromosome 11 and chromosome 9In this part, we described the phenotype characteristics of 2 autosomal dominant inherited hearing impairment pedigrees (named Z029 and 686 respectively) for further genetic study. In the two pedigree, most affected individuals noticed hearing impairment after their twenties with subsequent gradual progression from moderate to profound loss involving from high frequencies to all frequencies. There were no obvious vestibular dysfunction and other associated abnormalities. We first performed gene mapping in chromosome 14 for the candidate gene COCH. The results ruled out the gene contributed to the Z029 and 686 hearing loss. Then, genome scan was carried out on the two pedigrees and mapped the gene to llql3.4-22.1 and 9p 13.2-13.3. This resulted in significant evidence for linkage to the markers D11S165-D11S1874 and D9S1314-D9S898 (two-point lod-score of 5.71 on marker D11S937 at theta=0.05 and 3.25 on D9S 1817 at theta=0.0) and a candidate critical region of DFNAll with hearing impairment gene(MYO7A) are located on our Z029 mapping region. But on 686 mapping locus,no known deaf genes or loci have been reported,then another new gene locus was found-DFNA55.So,our study maybe found one more causative deaf genes for the hereditary hearing loss.