Diseases

Deafness

Presbycusis is the common sensorineural hearing impairment in elderly persons. One third of people over sixty five years of age have some degree of deafness and forty percent or more of those over seventy-five have deafness. It usually occurs equally bilaterally, it is progressive, and begins with high tone deafness. It has a higher incidence amongst people having cardiovascular disease, high blood pressure, diabetes, and other circulatory problems. Deafness is a common feature of mitochondrial diseases. However, the progression of hearing loss is slow and a threshold level of the accumulated deletion is reached before cellular malfunction occurs. This may provide a useful therapeutic window for drug treatment.

Hearing impairment in mitochondrial disease may arise from end-organ dysfunction due to deficient energy release within the stria vascularis or hair cells, which are metabolically very active structures. There is a strong correlation between presbycusis in man and animals and the extent ofmitochondrial DNA deletions and mutations. Mitochondrial DNA mutations and deletions cause a reduction of mitochondrial oxidative phosphorylation, cochlear hypoxia and decreased auditory nerve function.

Mitochondrial cochlear deafness can be treated successfully by cochlear implants. Whether part of a systemic mitochondrial disease or occurring alone it could be treated by a drug preventing mitochondrial DNA damage.