Purpose: To determine the importance of genetic factors in age-related macular degeneration by using a twin study to compare the concordance of age-related macular degeneration in monozygotic and dizygotic twin pairs.
Methods: We prospectively examined 134 consecutive twin pairs and two triplet sets for age-related macular degeneration. The zygosity was determined by genetic laboratory tests.
Results: The concordance of age-related macular degeneration was 100% (25 of 25) in monozygotic and 42% (five of 12) in dizygotic twin pairs. The other twins or triplets had no macular changes of age-related macular degeneration.
Conclusions: The statistically significant higher concordance of age-related macular degeneration in monozygotic than in dizygotic twin pairs and the clinical heterogeneity of age-related macular degeneration strongly suggest the importance of genetic and nongenetic factors, respectively, in age-related macular degeneration.