In about 1775, a devastating typhoon swept over the island of Pingelap, a Pacific atoll that’s now part of Micronesia. Twenty people survived the storm and subsequent famine to repopulate the island. One man, however, apparently carried a genetic mutation that causes color blindness. Intermarriage among the survivors’ descendents has left about 5 percent of the island’s residents with the color blindness disease achromatopsia—all of whom trace their ancestry to this man. The disease also causes sensitivity to light and poor visual acuity.
Researchers have now pinpointed a mutation that results in achromatopsia in these people in a gene called CNGB3. DNA taken from the blood of 60 islanders whose families have a history of color blindness shows that the mutation induces cells to produce phenylalanine in the place of serine. Both are amino acids, but phenylalanine ends up disrupting photoreceptors in the eye, says study coauthor Olof H. Sundin of Johns Hopkins Medical Institutions in Baltimore.
The finding lays the groundwork for genetic screening on Pingelap, he says. Two people with normal sight but who carry the mutation pass on a one-in-four chance of color blindness to their offspring. However, a color-blind person and a noncarrier have no chance of having a color-blind child, he says.