Dr. Paul A. Sieving, director of the National Eye Institute, a part of the National Institutes of Health, said in the United States a disease is considered rare if it affects fewer than 200,000 Americans.
Scientists have identified more than 7,000 rare diseases, some of which affect only a few hundred people. Considered together, however, rare diseases affect 25 million Americans, which means about 1-in-every-10 people has one, Sieving said.
"Recent advances in gene technology are illuminating our understanding of the causes of rare diseases and quickening the translation of discoveries into new treatments," Seiving said in a statement. "National Eye Institute scientists have successfully used gene therapy to improve vision in people with Leber congenital amaurosis, a rare genetic disorder that causes blindness through the degeneration of photoreceptor cells -- the rods and cones in the layer of tissue in the back of the eye called the retina. Gene therapy helps restore gene function by inserting copies of normal, functioning genes into cells."
Although vision gains were modest, successful demonstration of the strategy holds promise for treating other degenerative retinal disorders such as retinitis pigmentosa, Sieving said.