title: Extremely low penetrance of hearing loss in four Chinese families with the mitochondrial 12S rRNA A1555G mutation.
abstract: Mutations in mitochondrial DNA (mtDNA) have been found to be associated with sensorineural hearing loss. We report here the clinical, genetic, and molecular characterization of four Chinese pedigrees with aminoglycoside-induced and nonsyndromic hearing impairment. Clinical evaluation revealed the variable phenotype of hearing impairment including audiometric configuration in these subjects, although these subjects share some common features: bilateral and sensorineural hearing impairment. Strikingly, these Chinese pedigrees exhibited extremely low penetrance of hearing loss (5.2%, 4.8%, 4.2%, and 13.3%, respectively, and with an average 8% penetrance). In particular, four of all five affected matrilineal relatives of these pedigrees had aminoglycoside-induced hearing loss. Sequence analysis of the complete mitochondrial genomes in these pedigrees showed the distinct sets of mtDNA polymorphism, in addition to the identical homoplasmic A1555G mutation, associated with hearing impairment in many families from different genetic backgrounds. The fact that mtDNA of those pedigrees belonged to different haplogroups R9a, N9a, D4a, and D4 suggested that the A1555G mutation occurred sporadically and multiplied through evolution of the mtDNA in China. However, there was the absence of functionally significant mutations in tRNA and rRNAs or secondary LHON mutations in these Chinese families. These data imply that the nuclear background or/and mitochondrial haplotype may not play a significant role in the phenotypic expression of the A1555G mutation in these Chinese pedigrees. However, aminoglycoside appears to be a major modifier factor for the phenotypic manifestation of the A1555G mutation in these Chinese families.
authors.affiliation: Institute of Otolaryngology, Chinese PLA General Hospital, Beijing, China. ywy301@263.net
authors.forename: Wie-Yen
authors.initials: WY
authors.lastname: Young
authors.forename: Lidong
authors.initials: L
authors.lastname: Zhao
authors.forename: Yaping
authors.initials: Y
authors.lastname: Qian
authors.forename: Qiuju
authors.initials: Q
authors.lastname: Wang
authors.forename: Ning
authors.initials: N
authors.lastname: Li
authors.forename: John H
authors.initials: JH
authors.lastname: Greinwald
authors.forename: Min-Xin
authors.initials: MX
authors.lastname: Guan
mesh_terms: D000328:Adult; D044466:Asian People / Q000706:statistics & numerical data; D002648:Child; D002675:Child, Preschool; D002681:China / Q000453:epidemiology; D004252:DNA Mutational Analysis; D004272:DNA, Mitochondrial / Q000235:genetics*; D005260:Female; D005787:Gene Frequency; D020022:Genetic Predisposition to Disease / Q000453:epidemiology / Q000235:genetics*; D006319:Hearing Loss, Sensorineural / Q000175:diagnosis* / Q000453:epidemiology / Q000235:genetics*; D006801:Humans; D008297:Male; D010375:Pedigree; D010641:Phenotype; D010802:Phylogeny; D011237:Predictive Value of Tests; D015995:Prevalence; D012335:RNA, Ribosomal / Q000235:genetics*; D012016:Reference Values; D018570:Risk Assessment / Q000379:methods*; D012307:Risk Factors; D012737:Sex Factors
chemical_list: D004272:DNA, Mitochondrial; D012335:RNA, Ribosomal; C075526:RNA, ribosomal, 12S