| Objective:Hearing loss is one of the most common sensory disorders in the humankind, which influences the ability of living, learning and communication of the deaf badly. Meanwhile it put on the family and the society a lot of pressure. According to WHO, hearing loss ranked the 15th place in the world disease list, while the 6th in Europe, the 10th in the western pacific and the 11th in the eastsouth Asian. It was estimated there was approximately 7 hundred million people with hearing loss over 50dB. The population with hearing loss over 25dB accounted for 1% in the youth, 10% in the population of 60 years old and 50% in the population of 75 years old. 1 in 1000 neonates was born with severe to profound hearing impairment, and the half of them were attributable to genetic causes. And 1% of these genetics causes was concerned with mitochondrial dysfunction. Therefore, the hearing impairment correlated with mitochondrial dysfunction occupies 5‰of the whole deaf people. It was estimated that 0.25 billion people in the world suffered over moderate hearing impairment, and in China the number of the disabled with hearing impairment amounted to 20,570 thousand. According to this ratio, there are 1250 thousand deaf patients due to mitochondrial dysfunction in the world, and 102,580 in China. Therefore, it meanes significant in the society and the economy to study the hearing impairment correlated with mitochondrial. And the mitochondrial DNA (mtDNA) A1555G mutation has been the hot spot for many years. Many investigation data had showed that mtDNA A1555G mutation was associated with the aminoglycoside antibiotics induced deafness(AAID). MtDNA A1555G mutation had been detected in both pedigrees members and sporadic cases. In China, many research reports had revealed that AAID ranked the first in the hearing impairment caused by the ototoxic drug. AmAn was the most important and frequent cause to induce disorders of the drug ototoxicity. Moreover,AmAn was gradually becoming the most principal one in all kinds of factors which caused both congenital deafness and acquired deafness in neonate and adult deafness. According to the relevant survey last century, 2/3 of the hearing impairments in more than 10 million deaf and dumb children resulted from the abuse of the ototoxic drug in our country. The investigation statistics in 1987 showed that AmAn ototoxicity accounted for 66% in all etiological factors in deaf and dumb children. In 1997 Zhensheng Chen pointed out the proportion rose to 84% by studing 812 deaf and dumb children from Chinese town and coutryside. In 2004, the Xinhua News Agency reported that 30 thousand children suffered hearing impairment in China per year according to the Department of Health. And 95% of these are attributed to the irregular use of AmAn.In order to understand the mutation frequency of the mtDNA A1555G in Jilin province and reduce the incidence of the deafness caused by drug, we detected mtDNA A1555G mutation of 129 NSHI students from Changchun deaf-mute school.Method:1,Subjects and clinical data: 129 NSHI students from Changchun deaf-mute school were selected , 73 males and 56 females, aged from 7 to 20 years old. All the subjects who were investigated with questionnaire were confirmed to be NSHI individuals (without middle ear diseases, cerebritis, cerebral meningitis, parotitis, pregnancy abnormity, hypoxia in birth, omotocia, dysgnosia, definite head injury before hearing loss). The questionnaire was consisted of basic information, deafness incidence, deafness causes (development, surgical trauma history, operation history , tympanitis and mother gestation in the students with deafness caused by drug ototoxicity), personal history, family history and other systematic diseases. A pure-tone audiometry(PTA) was performed to all the subjects. The inclusion criteria was bilateral severe to profound sensorial hearing impairment with the PTA examination.2,Empirical method: 129 NSHI students from Changchun deaf-mute school as the subjects were ascertained and 10 normal individuals as controls. Genomic DNA were extracted from whole blood of the participants. A pair of primers were designed according to the revelant literature. Subjects'DNA segments spanning mtDNA 1555 site were amplified using polymerase chain reaction (PCR) .For the detection of mtDNA A1555G mutation, the amplified segments were digested with a restriction enzyme Alw26I. The digested samples were then analyzed by electrophoresis through agarose gel.Results:DNA (containing mtDNA) from 129 subjects (including 37 patients with AmAn induced deafness ) of the Changchun deaf-mute school and 10 controls were amplified by PCR and detected by agarose gel electrophores. 463bp coding region bands were obtained. The amplified segments were digested with a restriction enzyme Alw26I and analyzed by agarose gel electrophoresis. 3 subjects exhibited abnormal band, 2 of which had been administered AmAn. This illustrated these 3 subjects incur mtDNA A1555G mutation. The other subjects and the controls presented with normal band. From these data it could be deduced that incidence of the mtDNA A1555G mutation among NSHI cases in Jilin province was 2.33% and 5.41% in the patients with AmAn induced deafness. Both of them were lower than the domestic average.Conclusion:1,By screening the NSHI students of Changchun deaf-mute school, it was concluded that the incidence of mtDNA A1555G mutation was 2.33% among the NSHI cases and 5.41% in the patients with AmAn induced deafness. Both of them were lower than the domestic average.2,It was significant to detect mtDNA A1555G mutation in prevention of deafness caused by the drug ototoxicity. The individuals hypersensitive to AmAn could be found by screening the high risk people or definite group for mtDNA A1555G mutation. By means of the early diagnosis and intervention performed to those who were hypersensitive to AmAn, the incidence of deafness caused by drug ototoxicity could descend considerably.
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