Hypothesis: We attempted to determine if the common mitochondrial DNA aging deletion is also associated with presbycusis.
Background: Presbycusis is the most common cause of deafness in adults in the United States, affecting approximately 40% of the population older than 75 years of age. The ability to identify a gene(s) or a specific genetic deficit(s) associated with presbycusis has significant clinical importance.
Methods: The current study examined mitochondrial DNA (mtDNA) from cochlear sections of 34 human temporal bones: 17 with normal hearing and 17 with presbycusis. DNA was extracted from celloidin-embedded temporal bone sections; and specific oligonucleotide primers were designed to amplify the cytochrome b gene and a 4,977 base pair (bp) deletion of the mtDNA. Polymerase chain reaction (PCR) was used to amplify the base pair products that correspond to targeted gene regions, and sequencing was used to verify the products.
Results: Fourteen of the 17 patients with hearing loss showed the 4,977 bp deletion and this deletion was present in only eight of the 17 human specimens with normal audiograms. The cytochrome b gene was amplified from all specimens.
Conclusions: The current study demonstrates the presence of a 4,977 bp deletion in human mitochondrial DNA genome that is associated with aging and with some forms of presbycusis. These results, coupled with previous animal studies, suggest that this 4,977 deletion may be associated with presbycusis.