Thursday, September 17, 2009

Color blindness a disease?

Two color blind adult monkeys have been cured of their 'disease' with gene therapy, as described in an online Nature story. The story is picked up by the BBC and Science Daily, among others. One of the investigators is quoted in Science Daily as follows,
"We've added red sensitivity to cone cells in animals that are born with a condition that is exactly like human color blindness," said William W. Hauswirth, Ph.D., a professor of ophthalmic molecular genetics at the UF College of Medicine and a member of the UF Genetics Institute and the Powell Gene Therapy Center. "Although color blindness is only moderately life-altering, we've shown we can cure a cone disease in a primate, and that it can be done very safely. That's extremely encouraging for the development of therapies for human cone diseases that really are blinding."
The researchers introduced genes that produce a protein called long-wavelength opsin into the monkeys' retinal cells via an adenovirus delivery system. The virus gets into the cell and the opsin gene it has been engineered to contain is expressed as a protein, which the cell then processes properly enough that it works to respond to the right light frequency. Apparently the monkeys began to see color for the first time about 20 weeks after the injection of the genes. Here's a video showing how the monkeys' newfound ability to see color was tested.

Color blindness is a nuisance, though perhaps a non-trivial one when it comes to seeing traffic lights or other alerts, but many people live very successful lives without being able to see red or green. But, if gene therapy can cure other forms of blindness associated with cone cells, as Dr Hauswirth suggests, this is good news indeed.

However, the story in Science Daily goes on to say that

[t]he finding is ... likely to intrigue millions of people around the world who are colorblind, including about 3.5 million people in the United States, more than 13 million in India and more than 16 million in China. The problem mostly affects men, leaving about 8 percent of Caucasian men in the United States incapable of discerning red and green hues that are important for everyday things like recognizing traffic lights.

The reason that more men than women are color blind is that these color-sensing genes are on the X chromosome, and males only have one X, so that if they have a defective gene, all their cone cells will bear the defect. Women have two X's (that's what makes them female), and though each retinal cell only randomly picks one of the two to use, a woman carrying a mutant opsin gene will have half her retinal cells using the normal, functioning gene (it's rare for both to have a mutation, since the mutations are fairly uncommon).

But, color blindness is part of the natural spectrum of color-sensitivity variation. It isn't a 'disease' and in a tight-budgeted time for health care, suggesting that millions of people might be interested in a 'cure' might seem to be an almost cynical disregarding of priorities. Given that the numbers of people who are color blind is much greater than the numbers of people with true blindness, are the researchers emphasizing color blindness in an attempt to interest pharmaceutical companies in this new technology, or has this slant been introduced by the journalists? Hard to tell. This could be another Viagra, a blockbuster cure for something that hasn't needed pharmacologicals before now. If this is what happens, it would show (or confirm) how utterly socially irresponsible the pharmas are, and the governments who allow this to be done.

On the other hand, if the technique works and could be used to treat real genetic retinal disease, it will be a boon to society and an excellent example of the fact that, for things that truly are genetic and relatively simple, genetic engineering should work. Curing any genetic form of blindness would be a major advance.

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