Association between the mitochondrial DNA 4977 common deletion in the hair shaft and hearing loss in presbycusis.

The aim of the present study was to examine the role of the mitochondrial (mt) DNA common deletion (CD) 4977 (mtDNACD4977) in the hair shaft in patients with presbycusis. A total of 87 individuals with presbycusis and 95 normal‑hearing controls were selected based on strict audiometric criteria. Nested polymerase chain reaction (PCR), sequencing and quantitative (q)PCR were used to examine the expression levels of mtDNACD4977 in the hair shaft in presbycusis. Nested PCR of the hair shaft demonstrated that 8/95 cases with normal hearing were found to be positive for mtDNACD4977, as compared with 59/87 cases in the presbycusis group. The mtDNACD4977 was positive in 22/43 cases with mild‑to‑moderate hearing loss, 25/31 cases with moderate‑to‑severe, severe hearing loss, and 12/13 cases with profound deafness. Statistically significant differences in mtDNACD4977 expression were identified among all of the groups (P<0.001). The sequencing and qPCR assays demonstrated a trend towards an increase in the mean CD level of mtDNACD4977 with a more severe hearing loss at 8 kHz (r=0.778, P<0.001) and all ranges of frequency (r=0.858, P<0.001). In conclusion, the present study demonstrates a correlation between mtDNACD4977 in the human hair shaft and the severity of hearing loss in presbycusis.