Treatment for X-linked RP in Dogs
14 May 2012
Researchers from the University of Pennsylvania in the United States have developed a treatment for X-Linked Retinitis Pigmentosa (XLRP) in dogs. Their success in treating the initial study group also holds promise for treating XLRP in humans.
A healthy retina converts the light coming into the eye into images. In RP, the retina either fails to develop, or degenerates at an early stage. Loss of night vision is often the first sign of RP in dogs.
The genetic mutation which causes this may be autosomal recessive (two copies of the defective gene must be present), autosomal dominant (only one defective gene is necessary to cause the problem) or X-linked (the defect is found on an X chromosome).
The XLRP form of RP in dogs is found in Siberian huskies, but is rare in other breeds. The results of this XLRP study are particularly encouraging for human medicine as XLRP is more common in people.
Treating XLRP With Viral Vector Gene Therapy
One of the important aspects of the trial conducted at the University of Pennsylvania is that both types of photoreceptor cells in the retina were treated, while in previous work, only rods or cones were targeted. In order to restore vision, the researchers used a single subretinal injection of healthy Retinitis Pigmentosa GTPase Regulator (RPGR) gene, which is generally the damaged one in XLRP.
To ensure that the RPGR was delivered to the diseased rods and cones, a viral vector which targets rods and cones and not other cells was used. In addition, a bit of genetic code, or “promotor,” was attached to the healthy RPGR gene ensuring the gene would only activate if the virus entered the appropriate cells.
If the results of this trial can be repeated, it will mean that it is possible to prevent the development of XLRP in dogs and perhaps people with the genetic mutation.
A leading researcher at Moorfields said "This is exciting news - the work is from a very good grouping and is an important step on the road to therapy for X-linked RP. But it also illustrates how difficult it can be; they tried several approaches and only some worked."
What is even more notable is that the treatment appears to restore damaged rods and cones in cases where the disease has progressed. Drs. Beltran and Aguirre were also able to show that the treatment repaired connections to other neurons which send signals from the retina to the brain, which makes it promising for other types of RP where changes in the retinal neurons are a factor.
It is important to remember, however, that this is a preliminary study, using a small number of dogs. Longer term testing and then clinical trials will be needed to ensure the treatment is safe and effective under a variety of circumstances. |
