How is deafness inherited?
The role of mitochondrial DNA in the pathogenesis of hearing loss

Dr Carolyn Sue, Royal North Shore Hospital

Dr Carolyn Sue completed three years of post-doctoral training at Columbia University, New York and has recently joined the Department of Neurology at Royal North Shore Hospital. Dr Sue has been allocated laboratory space and technical assistance, but, she says “funding for start up projects is limited, and that is where the Brain Foundation comes in.”

Hearing loss is an extremely common and under-studied age-related disability, affecting 39% of Australians aged 50 years or older. Both genetic and environmental factors may contribute to the development of age-related hearing loss. Dr Sue wanted to investigate the role that genetic factors may play in development of hearing loss.

Human genetic material (DNA) resides in two places in body cells; the nucleus and in other parts of the cell called mitochondria. These mitochondria are derived from bacteria that were engulfed by the cell back in primordial life. Although this genetic material is different to nuclear DNA, it has an essential role in helping to provide energy for the cell.

This project investigated the role that mitochondrial DNA played in the development of hearing loss in subjects in the Australian community. In this study, we found that mutations in this type of DNA were associated with age-related hearing loss.  We are now analysing our data to detect other risk factors that could be modified to reduce the chance of developing hearing loss in individuals with these genetic abnormalities.

Dr Sue has previously been the recipient of Brain Foundation grants for work related to mitochondrial DNA.  In 2001 she was awarded funding for the purchase of a dedicated tissue culture hood. This was used to grow cells for a project on “Comparison of Bioenergetic Defects and Induction of Cell Death Pathways in Nuclear and Mitochondrial DNA – Encoded Disorders”. Preliminary results were presented to the Westmead Hospital Research Symposium (August 2001), and the work was awarded the prize for Best Poster presentation (Shepherd and Sue, Westmead Research Week Abstract Book 2001). The research assistant employed in the laboratory has now converted to a PhD and has taken on the work as her thesis project.