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Cataracts: Genes vs. age and environment
By Bijal P. Trivedi

Genes play a greater role in cataract formation than do age and environment, according to a new study published in this week's issue of The New England Journal of Medicine.

Past research has focused on age, smoking and gender as the greatest risk factors for cataracts, but the genetic contribution has not been closely examined until now.

The authors of the report studied 506 pairs of female twins, with an average age of 62, and measured the extent of cataract formation. Identical twins, who share an identical set of genes, had very similar cataracts, while there was greater variation in cataract development between non-identical twins who differ genetically.

A cataract refers to a lens that has become cloudy and opaque. The lens is responsible for focussing the light entering the eye on the retina. If a plastic transplant, which is the only treatment available for cataracts, does not replace the lens, blindness will ensue.

Based on this study, the researchers estimate that 48 percent of variation in cataracts is due to genes, 38 percent due to age, and only 14 percent due to environmental factors like smoking, diet, X-rays, or sunlight.

The authors point out that, as only British women were used in this study, the genetic contribution may vary among different races. The authors also suggest that there may be individual genes directly involved with cataract formation, which when identified could eventually lead to new treatments.

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Hammond, C.J. et al. Genetic and environmental factors in age-related nuclear cataracts in monozygotic and dizygotic twins. N Engl J Med 342, 1786-1790 (June 15, 2000).

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