title: Temporal bone histopathological and quantitative analysis of mitochondrial DNA in MELAS.
abstract: OBJECTIVE
  Although hearing loss is common in MELAS (syndrome of mitochondrial encephalopathy, lactic acidosis and stroke-like episodes), the histopathology of the temporal bone has not been reported. The majority of cases of MELAS are linked to a mitochondrial DNA (mtDNA) mutation at nucleotide 3243. In MELAS, normal mtDNA and mutant mtDNA coexist in a heteroplasmic manner. The purpose of the study was to report the otopathological findings from two patients with MELAS and quantitative mtDNA analysis in the inner ear of one of these patients.
  
  
  METHODS
  Basic scientific histopathological examination and quantitative mtDNA analysis of the temporal bone.
  
  
  METHODS
  Temporal bones were embedded in celloidin and sectioned for light microscopic study. Graphic reconstruction of the cochlea was performed using the method described by Schuknecht. For quantitative mtDNA analysis, total DNA from the membranous part of the inner ear was collected, amplified by polymerase chain reaction, and digested with the restriction enzyme. The percentage of mutant/total mtDNA was measured by the ratio of fluorescence intensity.
  
  
  RESULTS
  Histopathological examination revealed severe degeneration of the stria vascularis and degenerative change of spiral ganglion cells in both patients. The quantitative DNA studies showed that the proportion of mutant to wild-type mtDNA was similar in both histologically affected and histologically unaffected tissues within the inner ear.
  
  
  CONCLUSIONS
  Dysfunction of the stria vascularis and spiral ganglion cells causes sensorineural hearing loss in MELAS.
authors.affiliation: Department of Otolarynology, Gunma University, Maebashi, Japan.
authors.forename: Katsumasa
authors.initials: K
authors.lastname: Takahashi
authors.forename: Saumil N
authors.initials: SN
authors.lastname: Merchant
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Miyazawa
authors.forename: Toshikazu
authors.initials: T
authors.lastname: Yamaguchi
authors.forename: Michael J
authors.initials: MJ
authors.lastname: McKenna
authors.forename: Hiroko
authors.initials: H
authors.lastname: Kouda
authors.forename: Yukiko
authors.initials: Y
authors.lastname: Iino
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Someya
authors.forename: Yuya
authors.initials: Y
authors.lastname: Tamagawa
authors.forename: Yoshihisa
authors.initials: Y
authors.lastname: Takiyama
authors.forename: Imaharu
authors.initials: I
authors.lastname: Nakano
authors.forename: Ken
authors.initials: K
authors.lastname: Saito
authors.forename: Philip
authors.initials: P
authors.lastname: Boyer
authors.forename: Ken
authors.initials: K
authors.lastname: Kitamura
mesh_terms: D000328:Adult; D004252:DNA Mutational Analysis; D004272:DNA, Mitochondrial / Q000235:genetics*; D007758:Ear, Inner / Q000737:chemistry / Q000473:pathology*; D005260:Female; D006319:Hearing Loss, Sensorineural / Q000150:complications; D006801:Humans; D017241:MELAS Syndrome / Q000150:complications / Q000235:genetics* / Q000473:pathology*; D009154:Mutation; D013701:Temporal Bone / Q000737:chemistry / Q000473:pathology*
chemical_list: D004272:DNA, Mitochondrial