May 4, 2014

One Year Results of Choroideremia Gene Therapy Trial

In January, follow-up results from the first six months of the British choroideremia gene therapy trial were published. At the Association for Vision Research and Ophthalmology meeting today, the team led by Dr. Robert MacLaren and Dr. Miguel Seabra presented the outcomes for the first year of the study.

Once again, Dr. MacLaren and colleagues reported on the effect of gene therapy on retinal and visual function in six patients aged 35–63 years with different stages of choroideremia. Choroideremia is a condition that develops slowly with the most severe effects occurring late in life. It is caused by mutations in the gene REP1 and the loss of the protein that gene would normally make. Four of the men treated in the study had near normal visual acuity, while two had more severe vision loss.

In the six month results quite dramatic improvements in vision were reported for the two men who had entered the study with the most severe vision loss.  Both could read several more lines from a standard eye chart. These benefits have remained stable, after a year, with both participants reading 4 additional lines on a standard eye chart, compared to their abilities before the surgery.

At six months, it had been more difficult to verify visual changes for the four men with fairly good vision when they entered the trial. However, a year following treatment there are very promising signs that vision loss in these men has slowed. All of the study participants had improved sensitivity to light in the treated retina, compared to the retina of the untreated eye.

In people with degenerative retinal disease like choroideremia, the retina continually gets thinner as the damage proceeds. None of these men have had any significant retinal thinning over the first year of the study, although two of them did have cataracts which progressed somewhat over the course of the trial.

These results continue to suggest that the therapy is capable of protecting vision similar to what would have been predicted from earlier animal studies. However, we still can’t know the long-term risks or benefits of this type of therapy.

A trial of the same therapy has been funded at the University of Alberta under the direction of Dr. Ian MacDonald. Potential participants are currently being screened at the Canadian site, and first Canadian patients will be treated later this year.