New theory about color blindness

Copyright © 1999 Nando Media
Copyright © 1999 Associated Press
NEW YORK (May 3, 1999 12:48 a.m. EDT http://www.nandotimes.com)

Scientists in Washington state say they've solved a mystery behind a common form of color-blindness. One expert, however, is skeptical. About one in 20 American men has the red-green color-blind condition called deuteranomaly. The severity varies widely, but affected men may have trouble distinguishing between pink and blue-green, for example, or pink and white.

The basic problem is that a gene that lets the retina create a green-sensitive pigment fails to work. Sometimes that "green" gene is damaged or missing, but in most cases the gene is present and it's not clear why it is inactive. Researchers have also found an unusual "hybrid" gene in people with deuteranomaly and in people with normal vision. The gene is found in the same cluster that contains the green gene and its partner, a "red" gene.

Does this hybrid play any role in the condition? Only if it occupies a crucial place in the cluster, Samir Deeb and colleagues at the University of Washington in Seattle propose in the May issue of the journal Nature Genetics. They concluded that only the red gene and the gene next to it can function. If this adjacent gene is the "green" gene, vision is normal, they say. But if the hybrid gene occupies this second position, no green gene will get a chance to be turned on, they say.

In 10 people with deuteranomaly, they found that the hybrid gene was always in the second position. In two people with normal vision, the hybrid gene was in the third position. The researchers also found in three retinas from deceased people, the hybrid gene was active only when it was in the second position.

Maureen Neitz, an associate professor of opthalmology at the Medical College of Wisconsin, said she wasn't convinced. It's not proved that the hybrid gene was inactive in the third position, she said. She also said her own published work shows that more than three genes in a cluster can be active, rather than just the first two. Deeb replied he hasn't found more than two active genes per cluster in analyzing more than 70 retinas.