Gene therapy has been successfully used to restore vision in patients suffering from a rare genetic disorder. The nature of this disorder means that the therapy is much more successful in children than adults.
Children born with one form, LCA2, have defects in a gene called RPE65 that helps the retina’s light-sensing cells make rhodopsin, a pigment needed to absorb light. Without rhodopsin, the photoreceptor cells gradually die.
Gene therapy works by using a modified virus as a delivery system to get specific genes into specific areas. (Take a look at our article Is Chronic Fatigue Syndrome Caused By A Virus? for some background about how viruses work explained in plain English). Researchers first tested the therapy on dogs and found they could partially restore sight by using a virus loaded with the RPE65 gene. Then the researchers conducted a limited study on six young adult humans, which also resulted in sight improvements.
But the Penn researchers knew from their studies in animals that children should improve even more because they have more intact retinal tissue than adults do. Today in an online paper in The Lancet, their team and collaborators in Europe report full study results for three of the adults they treated earlier and nine more patients, including four children ages 8 to 11. The children gained more light sensitivity than the adults did–their light sensitivity increased as much as four orders of magnitude, versus one–and they made far fewer mistakes in an obstacle course.
This is one of those good news/bad news stories.
The bad news:
- Older individuals with this disorder have lost more tissue, and therefore the therapy can be significantly less effective.
- This therapy only applies to blindness caused by a specific defective gene, and will not benefit someone suffering from any other type of blindness.
Now, the good news:
- Gene therapy sounds great in theory but has had few successes in real life applications. The success of this study will serve as boost to continue research into gene therapy.
- Other vision diseases are caused by genetic defects. In the near future it may be possible to do a simple blood test to determine which defective gene a child has and then apply the appropriate therapy to prevent a loss of vision from occurring in the first place.
There is a lot of excitement in the air because of the successful results. Take a look here to see a video of one of the patients, Cory Haas, breezing through an obstacle course a mere three months after therapy.
The LCA2 trials are a rare success for the field of gene therapy, which has also cured children with the immune disorder known as bubble boy disease. And they should pave the way for treating more vision disorders. “It’s an incredible launching pad to be able to target other diseases,” says Penn gene therapy researcher Jean Bennett, who led the study.
Showing that the LCA2 gene therapy treatment works best in children is “a big step” for inherited blindness, says geneticist Frans Cremers of Radboud University Nijmegen Medical Center in the Netherlands, who wrote an accompanying commentary in The Lancet. He notes that eight other vision diseases, including retinitis pigmentosa, have now been treated in mice and are ready to be tested in people. The challenge, he says, will be to expand genetic testing of people with blindness so as to find enough eligible patients for clinical trials of these rare disorders.