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      The potential role for use of mitochondrial DNA copy number as predictive biomarker in presbycusis

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          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.


          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.


          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).


          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.

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          Most cited references 42

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          Mitochondrial content reflects oocyte variability and fertilization outcome.

          To determine the content of mitochondrial DNA (mtDNA) in oocytes from a range of patients with fertilization success and failure. Analysis of mtDNA content in fertilized and unfertilized oocytes and embryos by real-time polymerase chain reaction (PCR). University hospital infertility and research center. Fifty-four women seeking treatment for infertility. None. A total of 142 fertilized and unfertilized oocytes were classified into three main groups. Group I consisted of 35 fertilized oocytes from 21 patients; group II, 65 unfertilized oocytes from 36 patients; and group III, 42 degenerate oocytes from 23 patients. Mitochondrial DNA content was determined by SYBR Green real-time PCR-based assay. The mean mtDNA copy number for the fertilized oocytes was 250,454, whereas for the unfertilized group it was 163,698. There were significant differences for mtDNA copy number between the male factor and female factor infertility unfertilized oocytes and between the unexplained infertility and female factor infertility groups. The mean copy number for the degenerate oocyte group was 44,629, which was significantly different from the other subdivisions in this group. Mitochondrial DNA content is critical to fertilization outcome and serves as an important marker of oocyte quality, explaining some cases of fertilization failure.
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            Uses and abuses of hearing loss classification.

             P. Clark (1981)
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              Mitochondrial DNA and disease.

              Mitochondrial DNA (mtDNA) defects are a relatively common cause of inherited disease and have been implicated in both ageing and cancer. MtDNA encodes essential subunits of the mitochondrial respiratory chain and defects result in impaired oxidative phosphorylation (OXPHOS). Similar OXPHOS defects have been shown to be present in a number of neurodegenerative conditions, including Parkinson's disease, as well as in normal ageing human tissues. Additionally, a number of tumours have been shown to contain mtDNA mutations and an altered metabolic phenotype. In this review we outline the unique characteristics of mitochondrial genetics before detailing important pathological features of mtDNA diseases, focusing on adult neurological disease as well as the role of mtDNA mutations in neurodegenerative diseases, ageing and cancer. Copyright © 2011 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

                Author and article information

                Ther Clin Risk Manag
                Ther Clin Risk Manag
                Therapeutics and Clinical Risk Management
                Therapeutics and Clinical Risk Management
                Dove Medical Press
                19 October 2016
                : 12
                : 1573-1578
                [1 ]ENT and Head & Neck Research Center and Department, Iran University of Medical Sciences, Tehran, Iran
                [2 ]Cellular and Molecular Research Center, Biochemistry Department, Iran University of Medical Sciences, Tehran, Iran
                [3 ]Department of Medical Genetics, National Institute for Genetic Engineering and Biotechnology, Tehran, Iran
                [4 ]Skull base research center, Iran University of Medical Sciences, Tehran, Iran
                Author notes
                Correspondence: Mohammad Farhadi, ENT and Head & Neck Research Center and Department, Iran University of Medical Sciences, Hazrat Rasool Akram Hospital, Niayesh Street, Sattarkhan Street, Tehran, Iran, Tel +98 21 6655 2828, Fax +98 21 6652 5329, Email mfa.ent@ 123456gmail.com
                © 2016 Falah et al. This work is published and licensed by Dove Medical Press Limited

                The full terms of this license are available at https://www.dovepress.com/terms.php and incorporate the Creative Commons Attribution – Non Commercial (unported, v3.0) License ( http://creativecommons.org/licenses/by-nc/3.0/). By accessing the work you hereby accept the Terms. Non-commercial uses of the work are permitted without any further permission from Dove Medical Press Limited, provided the work is properly attributed.

                Original Research


                age-related hearing impairment, presbycusis, biomarker, mtdna


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