After years of basic research, scientists at Johannes Gutenberg University Mainz (JGU) are increasingly able to understand the mechanisms underlying the human Usher syndrome and are coming ever closer to finding a successful treatment approach. The scientists in the Usher research group of Professor Dr. Uwe Wolfrum are evaluating two different strategies. These involve either the repair of mutated genes or the deactivation of the genetic defects using agents. Based on results obtained to date, both options seem promising. Usher syndrome is a congenital disorder that causes the loss of both hearing and vision.
Usher syndrome is the most common form of congenital deaf-blindness in humans, occurring in 1 in 6,000 of the population. Those suffering from the disease are drastically handicapped in everyday life as they lose the use of the two most important sensory organs, i.e., their ears and eyes. In the most severe cases, patients are born deaf and begin to suffer from vision impairment in the form of retinal degeneration in puberty that result in complete blindness. While it is possible to compensate for the loss of hearing with hearing aids and cochlear implants, no therapy was previously available for the ophthalmic component of the disorder. Scientists at Mainz University are currently undertaking preclinical translational research in an attempt to find an answer to this problem.
The investigations undertaken by the team of Dr. Kerstin Nagel-Wolfrum focused on the nonsense mutation in the USH1C gene that had been identified as the cause of the most severe form of Usher syndrome in a German family. The nonsense mutation is a stop signal generated by the DNA that causes premature termination of synthesis of the protein harmonin, which is encoded by USH1C.
The research team published its latest findings with regard to gene repair as a possible treatment of Usher syndrome in the June edition of the opthalmologic journal Investigative Opthalmology & Visual Science. During her doctoral research, Dr. Nora Overlack managed to repair the USH1C gene with the help of molecular scissors' generated using the so-called zinc-finger nuclease technique. Using zinc-finger nuclease, the scientists first initiated a double sequence DNA cleavage at the site of the disease-generating mutation. This surgical incision on the molecular level was then repaired by means of the cell's own repair mechanism in the form of homologous recombination and the introduction of a non-mutated USH1C DNA sequence. The mutated gene sequence was thus replaced with the non-mutated sequence. The efficacy of the zinc-finger nuclease technique with regard to genetic repair was demonstrated in a cell culture model at both the genome and the protein level.