irs in which one or both twins had AMD, 55 percent of MZ pairs were classified as concordant (at the same level of severity) whereas 25 percent of DZ pairs were concordant for AMD," the authors write. "For advanced disease, the corresponding concordance rates were 18 percent for MZ twin pairs and 6 percent for DZ 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," the researchers found. "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."

"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 conclude. "This twin study underscores the need for a multifactorial approach that incorporates genetic, environmental, and biologic factors in the study of the pathogenesis and clinical management of this increasingly prevalent cause of blindness."

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Contact: Mary Leach
617-573-4170
JAMA and Archives Journals
14-Mar-2005

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