Quantification of the Mitochondrial DNA Common Deletion in Presbycusis

Objectives/Hypothesis: This study was conducted to evaluate the association between the mitochondrial DNA (mtDNA) common deletion (CD) level in cochlear tissue and the severity of hearing loss in individuals with presbycusis. Study Design: Nineteen individuals with presbycusis, ranging from 60 to 87 years of age, who met strict audiometric criteria were compared with four age frequency-matched normal hearing controls ranging from 51 to 76 years of age. Five additional normal hearing individuals, ranging from 9 to 50 years of age, were also studied. Methods: A duplex real time polymerase chain reaction assay was used to quantify the mtDNA in archival cochlear tissue samples. Linear regression models were used for comparison of the CD level between groups. Results: The presbycusis group had a mean CD level of 32% with a standard deviation of 14%, and the normal hearing age matched control group had a mean CD level of 12% with a standard deviation of 2%. This difference in CD levels reached statistical significance (P = .011) and remained significant after adjusting for any differences in age between the two groups (age-adjusted P = .007). Furthermore, there was evidence for a significant association between the CD level and the severity of hearing loss based on audiometric thresholds at 8 kHz (r = 0.44, P = .034; age-adjusted partial correlation = 0.55, P = .007). Conclusions: For the first time, to our knowledge, these results demonstrate a relationship between quantitatively measured levels of the CD in human cochlear tissue and the severity of hearing loss in individuals with presbycusis.