Corneal dystrophy genes mapped.

Nearly 60 years ago, German scientist Alois Meesmann identified a hereditary eye disease that causes irritation, blurry vision, and sensitivity to light. Now, researchers have tracked descendants of the German group Meesmann originally studied, as well as two extended families in Northern Ireland that carry the trait. By means of eye examinations and tissue samples, they have discovered that genetic mutations in either of two genes are responsible for the disease, which has come to be known as Meesmann's corneal dystrophy.

In this disease, tiny round cysts form on the cornea and begin to rupture during adulthood. People with the condition usually cannot tolerate contact lenses, although some people who carry the mutated genes show few effects. Gene mapping opens the door to genetic testing for this corneal dystrophy, which carriers pass on to roughly half of their children, says W.H. Irwin McLean of Thomas Jefferson Medical College in Philadelphia. He and his colleagues in Germany and Northern Ireland report their findings in the May Nature Genetics.

The flawed gene causes a crucial error in the sequence of amino acids of some keratins--tough proteins that form protective surfaces for mammals' cells, especially on exposed outer parts of the body, including the eyeball. Without the normal, sturdy keratins, cells in the cornea are weakened and cysts form.

Not everyone who cannot tolerate contact lenses has corneal dystrophy. The genetic mapping may help future research on these people, who the researchers suspect have a genetic mutation that creates a milder abnormality. Also, the study "brings us closer to the complete picture of these protein mutations," McLean says, which could aid research into other keratin disorders.