Mapping And Cloning The Causative Genes In Chinese Pedigrees With Hereditary Hearing Loss And Molecular Epidemiology Of Connexins In Sporadic Population With Hereditary Hearing Loss

Over the past 10 years, remarkable progress has been made in the identification of new loci for non-syndromic hearing impairment (NSHI) and in the cloning of deafness genes. Since the first deafness gene was cloned in 1995, 39 genes for non-syndromic hearing loss have been identified. These genes encode a wide variety of protein classes: from myosins and other cytoskeletal proteins, channels and gap junction components, to transcription factors, extracellular matrix proteins and unknown proteins. These findings offer the promise to significantly expand our knowledge on the molecular mechanisms underlying the auditory and vestibular functions and on the pathophysiological mechanisms for hearing loss. With the completion of Human Genome Project, the release of massive genome sequence and function information, the advances in statistical genetics, and the use of the high-dense genetic markers provide powerful tool/information for genetic cloning and molecular epidemiology of human deafness.. This study used the plenty genetic resources established by the Otolaryngology Institute of PLA General Hospital, to hunt for the causative genes in three large Chinese pedigrees with non-syndromic hearing loss; and to investigate the molecular epidemiology of connexins in Chinese sporadic hearing-impaired cases. This thesis is divided into two main parts to present the results for the study.Part one: mapping and mutation screening of the causativeloci/genes in three hereditary hearing loss familiesThe purpose of this study was to map and to screen the genetic variants that cosegregated with the hereditary hearing loss in the three families.1. A causative gene was found in an X-linked congenital profound hearing loss familyThe clinic phenotype in family 021 was congenital profound hearing loss. The clinical investigations revealed the striking feature of the extremely high penetrance of deaf-mutism in the male members, but no penetrance in the female members. Linkage analysis was thus carried out under an X-link inheritance mode, with penetrance of 90%. The identified critical region spans a 29.53 cM region flanked by markers DXS983 and DXS1220. Maximal lod score of 3.21(theta=0.0) was observed at marker DXS990. Mutation screening of POU3F4 gene was conducted in family 021. A missense mutation (925T—C) was detected in all male patients, and in female carriers. The same mutation was not detected in other members of family 021 and in 110 unrelated controls with normal hearing. This mutation situated at POU homeodomain, was predicted to cause a conservative amino acid substitution (Ser309Pro). These data suggest that this mutation is responsible for the hearing loss in family 021.In short, a novel mutation of POU3F4 gene was identified to be the causative reason for the hearing loss in family 021. Further elucidation of the functional involvement of the mutation will help us to develop the method(s) for molecular diagnosis of the congenital hearing loss and to understand its role(s) in regulating the development of inner ear.2. AUNXl-a novel locus for auditory neuropathy was successfully mappedThe studied Family 015 was characterized with X-linked recessive non-syndromic auditory neuropathy. The disease locus for family 015 wasmapped into a chromosomal region defined by markers DXS1220 and DXS8084 via linkage analysis. Maximal lod score of 2.33 was observed at markers DXS1001, DXS1212, and DXS1211. The critical region spans a 28.09 cM chromosomal fragment. No known deaf genes or loci are localized within this region. Thus, AUNX1 (auditory neuropathy, X chromosome, locus 1) is a novel disease locus, and was approved by the International Committee of Human Genome Nomenclature.In short, a new locus (AUNX1) for non-syndromic auditory neuropathy was successfully mapped onto X chromosome using a large Chinese family.3. Mapping a disease locus for an autosomal-dominant inherited low-frequency sensorineural hearing loss (LFSNHL)Family 013 exhibited an autosomal dominant inheritance pattern of low frequency hearing loss. The disease locus was mapped into a chromosomal region flanked by markers D9S1677 to D9S1838 by linkage analysis. Maximal lod score of 4.57 was observed at marker D9S177. The region spans a 46.47 cM (28.54Mb) region. , containing DFNB31 and DFNB33 loci Because loci DFNB31 and DFNB33 follow a recessive mode(s) , the causative gene(s) underlying the low-frequency hearing loss in Family 013 might be in somewhere else.In short, we mapped low-frequency sensorineural hearing loss onto a chromosome 9 region via model-based linkage analysis of a well-characterized family. This region dose not overlaps any known loci for low-frequency hearing loss.Part two: molecular epidemiology of connexins was studied using Chinese sporadic hearing-impaired casesConnexin mutations were the major cause for autosomal recessive non-syndromic deafness (ARNSD). This study addressed the molecular...