The Clinical Features And Mutation Analysis Of The Responsible Genes For The Syndromic Hearing Impairment

In the past 10 years, there has been considerable growth in knowledge about hereditary hearing loss. To date, over 30 loci, 29 karyogenes and 2 chondriogenes had been identified for the syndromic hearing impairment (SHI) since the COL4A5 gene responsible for the Alport syndrome had been cloned in 1990. These genes encode a wide range of proteins varied from ionophorous protein, membrane protein, transcription factor to structural protein and so on. Usher syndrome and Waardenburg syndrome are thought to be the most common diseases in the SHI. Both Usher syndrome and Waardenburg syndrome are highly genetic heterogenous. Molecular basis for over 400 families with Usher syndrome and 80 families with Waardenburg syndrome had been revealed in European and American population. However, no correlated research had been carried out in Chinese population which is account for 1/5 of population in the world. Patients with Usher syndrome and Waardenburg syndrome were recruited by the Network established by the Institute of Otolaryngological of the Chinese PLA General Hospital. Genetic analysis was performed in responsible genes to identify the mutations in these patients.Part one: Clinical features and genetic aspects of the patients with Waardenburg syndromeWaardenburg syndrome (WS) is a typical auditory-pigmentary syndrome, with affected people showing varying combinations of sensorineural hearing loss and patchy abnormal pigmentation of the eyes, hair and skin. It is inherited as an autosomal dominant condition with incomplete penetrance and is divided into four subtypes according to its clinical features, WS1, WS2, WS3 and WS4. WS1 and WS2 are the most common types in WS. WS1 is caused by mutations in the PAX3gene, type 2 is caused by MITF gene mutations. In order to explore the molecular basis for WS in Chinese population, From Sep, 2004 to Dec, 2005, 35 patients with WS were recruited from 9 provinces and one autonomous region in China. Twenty-eight were WS2 and seven were WS1. High clinical variability was observed in WS1 and WS2 patients. Five out of six, 328C->T/(R110X), 763C-^T/(R255X), 20A-+G/(Y7C), 649A-+G/(R217G) and 332C-+T /(AlllV)were novel mutations we identified by mutation screening for MITF gene in all of WS2 patients, We confirmed 647-649deIGAA/del(R217) mutation, which was previously detected in one American family with Tietz syndrome (albinism- deafness syndrome) in European population.Mutation analysis of PAX3 gene in 7 WS1 patients was carried out. A novel mutation, 626-627delCT/(S209X) mutation was identified in one WS1 patient. 667C->T/(R223X) and 812G-?A/(R271H) mutations, which were previously reported in two American and European families, were confirmed in Chinese population. Two novel single base substitutions in intron sequence, IVS2+74T-+C and IVS6+57C->T were identified in two WS1 patients, respectively.In this study, eleven sequence changes, which add more data to the mutation database of MITF and PAX3 gene, were identified in Chinses WS1 and WS2 patients. Methods to perform genetic testing for WS patients were established.Part two: Genetic analysis of USH2A gene in a Chinese family with Usher syndrom type2Usher syndrome is the most common cause of deaf-blindness. It was characterized by sensorineural hearing loss and retinitis pigmentosa (RP), and was inherited in an autosomal recessive manner. According to the severity and progression of the hearing loss, the age at onset of RP, and the presence or absence of vestibular impairment, three clinical subtypes have been classified. Usher syndrome is clinically and genetically heterogeneous. Usher syndrome type2 (USH2) is the most common subtype in it. Three different loci have beenmapped and specific mutations in two genes have been detected in patients with USH2. Three molecular classification of USH2 named A, B and C type was made according to the genetic etiology. A family with affected family members suffered from deaf and progressive RP was diagnosed USH2 based on the diagnostic criteria for the USH2. A complete mutation analysis of the whole regions of the USH2A gene was performed in this family. No specific mutation, which was cosegragated with the phenotype of disease in this family, was identified. Nine single nucleotide polymorphisms (SNPs) of USH2A gene were identified. Four of them were firstly identified, including 573A-^G/(V191V), 1276A-VT/(N426Y), IVS19-44G—>A and IVS19-66A-+C. Five SNPs, which were previously reported in Eropean and American population, 504A->G/(T168T), 879T-?G/(L293L), IVS15+35G^A, IVS18-8T^G and 4457G-?A/(R1486K) were identified. Identification of these SNPs of USH2A gene play an important role in the research of mapping the distribution of polymorphic sites in the whole USH2A gene, constructing the haplotype analysis, and tracing the founder mutation in Chinese population. We will test for other previously mapped USH loci (USH2B, USH2C and USH3) using polymorphic markers specific for each locus.