BBC Science Correspondent Christine McGourty explains the development

Experts at the University of Michigan Medical School have been working with mice born with inner ear defects which cause deafness and balance problems.

By injecting normal DNA into the eggs of mice with inner ear defects they have managed to isolate the mutant gene which they believe causes their deafness.

Positive step

Sally Camper, associate professor of human genetics at the school, said: "Finding the defective gene is the first step toward developing new treatments which some day could restore hearing in children and adults."

Some deaf children will benefit from mice experiments

Once the gene was identified, scientists began work on introducing a normal version of the gene into the inner ears of people with mutant genes.

They believe that deafness is due to the gene's effect on an enzyme which controls sound frequency.

Wheat field

The enzyme is thought to help activate fibres in the inner ear which respond to changes in sound frequency. The movement of the fibres is described as being like a field of wheat moving to the changes in wind speed and direction.

Through the movement, signals are sent to the auditory nerves which are translated into sound by the brain.