title: The potential role for use of mitochondrial DNA copy number as predictive biomarker in presbycusis.
abstract: OBJECTIVE
  Age-related hearing impairment, or presbycusis, is the most common communication disorder and neurodegenerative disease in the elderly. Its prevalence is expected to increase, due to the trend of growth of the elderly population. The current diagnostic test for detection of presbycusis is implemented after there has been a change in hearing sensitivity. Identification of a pre-diagnostic biomarker would raise the possibility of preserving hearing sensitivity before damage occurs. Mitochondrial dysfunction, including the production of reactive oxygen species and induction of expression of apoptotic genes, participates in the progression of presbycusis. Mitochondrial DNA sequence variation has a critical role in presbycusis. However, the nature of the relationship between mitochondrial DNA copy number, an important biomarker in many other diseases, and presbycusis is undetermined.
  
  
  METHODS
  Fifty-four subjects with presbycusis and 29 healthy controls were selected after ear, nose, throat examination and pure-tone audiometry. DNA was extracted from peripheral blood samples. The copy number of mitochondrial DNA relative to the nuclear genome was measured by quantitative real-time polymerase chain reaction.
  
  
  RESULTS
  Subjects with presbycusis had a lower median mitochondrial DNA copy number than healthy subjects and the difference was statistically significant (P=0.007). Mitochondrial DNA copy number was also significantly associated with degree of hearing impairment (P=0.025) and audiogram configuration (P=0.022).
  
  
  CONCLUSIONS
  The findings of this study suggest that lower mitochondrial DNA copy number is responsible for presbycusis through alteration of mitochondrial function. Moreover, the significant association of mitochondrial DNA copy number in peripheral blood samples with the degree of hearing impairment and audiogram configuration has potential for use as a standard test for presbycusis, providing the possibility of the development of an easy-to-use biomarker for the early detection of this condition.
authors: ENT and Head & Neck Research Center and Department, Iran University of Medical Sciences, Tehran, Iran; Cellular and Molecular Research Center, Biochemistry Department, Iran University of Medical Sciences, Tehran, Iran.
authors: Masoumeh
authors: M
authors: Falah
authors: Department of Medical Genetics, National Institute for Genetic Engineering and Biotechnology, Tehran, Iran.
authors: Massoud
authors: M
authors: Houshmand
authors: Cellular and Molecular Research Center, Biochemistry Department, Iran University of Medical Sciences, Tehran, Iran.
authors: Mohammad
authors: M
authors: Najafi
authors: ENT and Head & Neck Research Center and Department, Iran University of Medical Sciences, Tehran, Iran.
authors: Maryam
authors: M
authors: Balali
authors: ENT and Head & Neck Research Center and Department, Iran University of Medical Sciences, Tehran, Iran.
authors: Saeid
authors: S
authors: Mahmoudian
authors: Skull base research center, Iran University of Medical Sciences, Tehran, Iran.
authors: Alimohamad
authors: A
authors: Asghari
authors: ENT and Head & Neck Research Center and Department, Iran University of Medical Sciences, Tehran, Iran.
authors: Hessamaldin
authors: H
authors: Emamdjomeh
authors: ENT and Head & Neck Research Center and Department, Iran University of Medical Sciences, Tehran, Iran.
authors: Mohammad
authors: M
authors: Farhadi
keywords: age-related hearing impairment; biomarker; mtDNA; presbycusis