Usher Syndrome is a rare hereditary disorder. The children suffering from this disorder are born deaf or hard of hearing and apart from night-blindness they also experience a progressive loss of eyesight. Eventually, people suffering from Usher Syndrome become both deaf and blind. Usher Syndrome is the most common type of hereditary deaf-blindness. There is no treatment yet that can stop the deterioration of both hearing and eyesight, but there is hope.
Although more than half of all people suffering from Usher Syndrome have mutations in the USH2A gene, this gene is not a target in the current studies into the development of gene replacement therapy. This is because of the size of the protein coding sequence of the USH2A gene (>15,000 bases!). A DNA fragment of such a length does simply not fit into the currently used gene therapeutic vectors (harmless viruses used for packaging genetic material and delivering this at its destination).
Minigenes: the solution for the problem?
In the ‘minigenes’ project, the USH2A gene is artificially made smaller by taking specific parts of the gene and sticking these together (= minigene). This makes it possible to insert these minigenes into the current vectors for use in genetic therapy.
In this project the therapeutic effect of shortened USH2A protein variants will be tested in the zebrafish model. If this is successful, this project may lead to a pre-clinical treatment method for USH2A-related retina degeneration, with which the deterioration of the eyesight could be stopped (within 5 to 10 years). This will have a tremendously positive impact on the quality of life of individual patients. The treatment can be applied to all people suffering from Usher Syndrome.
Stichting Ushersyndroom wants to finance scientific research that offers hope to all people suffering from Usher Syndrome and give a positive impulse to the ‘minigene’ research with an amount of €35,000. The remaining amount was supplemented by ENT Radboudumc. This is guaranteed and so ensures completion of the first phase of this study.
hope for all people
suffering from Usher Syndrome”
Time-consuming and specific
In the Radboudumc, researchers are also conducting other studies that may offer solutions for smaller groups of people with specific mutations in the USH2A gene. However, this study, which tests the therapeutic potential of exon skipping, is a very time-consuming study as a specific treatment is to be developed for each mutated exon. All the more because over 500 different mutations have been identified in the USH2A and these are spread over the entire gene. Even when the developments in the ‘exon skipping’ study show positive progress, this method still does not offer a solution for a significant part of the people with a mutation in the USH2A gene, because the build-up of the gene and protein are not suitable for this.
Recently, a joint venture was entered into with a pharmaceutical company for further development of this exon skipping method into a possible first trial in a few years.
SWODB also made a donation for financing a part of the ‘exon skipping’ study
Start-up Usher Syndrome database
In view of all developments concerning the research into Usher Syndrome it is really necessary to start the ‘Usher Database’ project. First of all, the Usher database is an essential collection of personal data, genetic data and extensive clinical data obtained by conducting a broad set of eyesight and hearing studies. The results of the most recent studies help to make an overview of the natural deterioration of eyesight and hearing of all people suffering from Usher Syndrome. These data will form the basis for future trials during which gene-therapeutic interventions can be tested and compared with this natural deterioration. Secondly, by studying these data an explanation can be found for the huge variation that is found in the clinical picture (even within families sharing the same genetic background).
Therefore the Usher database goes much beyond the national RD5000 database, in which at this moment only genetic and personal data of patients with hereditary retina degeneration are stored.
Usher Syndrome Foundation will concentrate on acquiring funds for the start-up of this project. Without this study and the Usher database the trials of gene-replacement therapies, which may be developed in a couple of years, cannot start either.
Minigenes USH2a: What is the status of this investigation?