TUESDAY, March 15, 2005 (HealthDay News) -- Genetics play a major role in age-related macular degeneration (AMD), one of the leading causes of blindness in older adults, says a Harvard Medical School study in the March issue of the journal Archives of Ophthalmology.
Researchers surveyed 840 male twins born between 1917 and 1927. The group included 210 identical twin pairs, 181 fraternal twin pairs and 58 others whose twin siblings were deceased or unavailable for the study.
All the study participants completed a survey and were examined for AMD -- 331 had no signs of AMD, 241 had early signs, 162 had intermediate AMD and 106 had advanced AMD. There were no differences in AMD rates between identical and fraternal twins. However, there were differences in severity.
The study found that among pairs in which one or both twins had AMD, 55 percent of identical twin pairs were classified as concordant (the same level of AMD severity), compared with 25 percent of fraternal twin pairs with AMD. For advanced AMD, the corresponding concordance rates were 18 percent for identical twin pairs and 6 percent for fraternal twin pairs.
"Genetic factors play a substantial role in the etiology (the cause of a disease) of AMD and associated macular characteristics, explaining 46 to 71 percent of the variation in the overall severity of the disease. Environmental factors unique to each twin were estimated to account for 19 to 37 percent of the variation in AMD grade (level of severity) and 28 to 64 percent of the variation in the specific macular measures," the study authors wrote.
"In summary, based on what is, to our knowledge, the largest twin study of AMD to date and the only population based twin registry in the United States among elderly individuals, we quantified substantial genetic influences on AMD, contributed new information about the heritability of advanced AMD, and established an important environmental contribution," the authors wrote.
More information
The U.S. National Eye Institute has more about AMD.
