Gene therapy of a rare form of deafness
Scientists cured deafness in mice with gene therapy
Dmitry Mazalev, Naked Science
According to a study by American and French scientists, deaf mice who received a new type of gene therapy developed the ability to hear at almost the same level as healthy ones. These results suggest that gene therapy may someday come to the rescue in cases previously untreatable.
Article by Akil et al. Dual AAV-mediated gene therapy restores hearing in a DFNB9 mouse model published in the journal PNAS.
More than half of cases of nonsyndromic deep congenital deafness have a genetic cause, and about 80 percent of them are caused by autosomal recessive forms of deafness. The mice in the experiment had so-called DFNB9 deafness, which accounts for two to eight percent of gene-related cases of deafness in humans. In deafness, a DFNB9 protein called otoferline cannot perform its usual function of transmitting sound information collected by thin hairs in the inner ear. However, after changing the genome of deaf mice with the help of specially created viruses, rodents gained the ability to hear almost as well as their relatives who were born with a normally functioning otoferline.
The structure of the human ear is schematically depicted on the left, and an immunofluorescence image of the auditory sensory epithelium is shown on the right. The inner hair cells having otoferline are colored green. A drawing from the press release of the Institut Pasteur Gene therapy permanently reverses genital deafness in mice.
Adeno-associated viruses (AAV) are considered to be one of the most promising vectors for therapeutic gene transfer in the treatment of diseases. AAV–based gene therapy is a promising method of treating deafness, but its use is limited by a potentially narrow therapeutic window: in humans, the development of the inner ear is completed in utero, and hearing becomes possible after about 20 weeks of pregnancy. In addition, genetic forms of congenital deafness are usually diagnosed during the newborn period, so the approach of gene therapy in animal models should take this into account, and the effectiveness of gene therapy should be demonstrated after gene injection, when the auditory system is already established. In other words, therapy will reverse the already existing deafness.
Meanwhile, scientists recognize that even after changing the same specific gene in mice that causes DFNB9 deafness in humans, it is too early to say that gene-editing viruses can be used to treat humans. There is quite a long way between animal experiments and human clinics, there are also some grounds for concern, therefore, before the technology gets practical application, the work of scientists must undergo several further studies.
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