Researchers from University of Iowa and Okayama University, Japan, have reported a possible cure for a kind of permanent hearing loss from parallel studies with animals.
The researchers gave a genetically deafened mouse interfering RNA that specifically prevents a gene from being expressed that would otherwise cause deafness. By preventing its expression, they had been able to prevent the deafness. Even at this early stage, the results are important feels the researchers because they point to other options for people who have hearing loss other than hearing aids or cochlear implants.
The gene-silencing technique used by the UI team is called RNA interference (RNAi) and works specifically against genetic conditions caused by a so-called dominant negative mechanism -- when a single copy of the mutant gene is sufficient to cause disease because the protein from the faulty gene has a dominant adverse effect over the protein from the normal gene. Several human forms of inherited deafness, including the one mimicked by the UI mouse model, are caused by a dominant negative mechanism.
To test the gene-silencing technique, the researchers had introduced a mutated gene that causes deafness in humans into the inner ear of mice. This gene acted through a dominant negative mechanism, and the mice had moderate hearing loss. Then they had simultaneously introduced the mutant gene and a short piece of interfering RNA specifically designed to silence the gene. Standard hearing tests, similar to those used on newborn babies, confirmed that the treated mice were able to hear.
The results said that RNA interference was not only successful but also highly specific. Despite the fact that the mouse and the human gene differed by only two nucleotides over the short stretch of gene targeted by the RNAi, the mutant human gene was silenced while the normal mouse gene was unaffected.
With a view to someday moving this therapy to humans, the researchers also developed a non-invasive strategy to deliver the RNAi. A small piece of foam soaked in a solution containing the interfering RNA was placed against the membrane covering one opening into the inner ear of the mice. The slightly porous membrane allowed the interfering RNA to diffuse into the inner ear cells.
Medindia on Hearing Loss: Further information:
Hearing loss: Losing the ability to hear sounds may be due to infection, blockage or damage to the ear. Other kinds of hearing loss may be due to damage to the pathway through which the sound waves travel from the hair cells of the inner ear to the auditory nerves. The probable causes of this may be age, disease, infections, tumor or stroke.
RNAi: RNA interference is a technique of gene silencing that is used to study the effect of absence of a gene, by causing disruption to its expression, on an animal or a plant.