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By Malcolm Ritter AP Science Writer

WASHINGTON, D.C. (June 26, 2000 – Associated Press)--- Scientists have identified the defective gene that causes a debilitating total colorblindness among many inhabitants of a tiny Pacific island.

Neurologist Oliver Sacks described the condition in the 1997 book "The Island of the Colorblind.'' The afflicted islanders see the world as if watching it on a black-and-white television set.

The discovery of the defective gene ends a 30-year search.

Researchers said it will not lead to a treatment immediately but might help find one eventually.

It could also lead to a test to tell islanders with normal vision whether they carry a flawed copy of the gene that would raise their children's risk of colorblindness.

The disorder appears only in people who inherit a flawed copy from each parent.

The island, Pingelap, is part of the Federated States of Micronesia.

Of the 3,000 Pingelapese, some of whom live on nearby islands, about one in 20 is totally colorblind. That compares with a worldwide rate of one in 50,000.

The flawed gene has been traced back to one man, who was among 20 survivors of a typhoon on Pingelap around 1775, who went on to re-establish the population.

The condition differs from the relatively common colorblindness in which people cannot distinguish certain colors. Affected people on the island cannot see colors at all. They lack the sharp vision most people use to read, and their eyes are overwhelmed by sunlight-- a particularly severe problem in the tropics.

In his book, Sacks noted that some affected islanders found work fishing by night.

"They're about as handicapped as you can be,'' said Dr. Irene Hussels Maumenee, a member of the research team that first formally described the condition on Pingelap in 1970.

"They stay in the cabin all day. They just don't see when they go out in the sunlight,'' said Maumenee, a professor of ophthalmology and pediatrics at the Johns Hopkins University School of Medicine.

Their difficulty in reading hampers their schoolwork, and "people consider them very much as an outcast,'' she said.

She is senior author of the paper announcing the finding of the gene, which appears in the July issue of the journal Nature Genetics.

Total colorblindness is called complete achromatopsia. One other flawed gene for the condition had been identified before, but it clearly was not responsible for the problem on Pingelap.

The discovery is "a really exciting result,'' said Maureen Neitz, who studies the genetics of colorblindness at the Medical College of Wisconsin.

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