Heredity of hard drusen in a population of twins aged 21–46 years

Abstract

Abstract: : Purpose: To determine the concordance rate for the presence of 10 or more small hard drusen in a population of healthy twins. Methods: Twins were recruited from the population–based Danish Twin Registry. Zygosity was determined from genetic markers. The study included 38 same–sex twin pairs (20 monozygotic and 18 dizygotic) with a mean age of 35±7½ (range 21–46) y and with an equal distribution of the two sexes on both zygosities. Fundus characteristics were visually assessed using digital fundus photography in red–free illumination (five 50 degree fields per eye) for the primary evaluation and color transparency photography (two 50 degree fields per eye) for supplementary evaluation. Every single hard drusen–compatible element (diameter <63 µm) anywhere in the fundus was visually identified, manually marked, and then registered in a computerized image database. Histogram stretching was allowed during the visual evaluation of the digital fundus photographs. For statistical analysis, the mean of the total drusen count in each of a subject's two eyes was used. Results: The median number of drusen per eye was 4 (range 0–150) in both monozygotic and dizygotic twins. Ten or more drusen per eye were found in 18 out of 76 subjects. The concordance rate for the absence or presence in an individual of a mean of 10 or more hard drusen per eye was 90% in monozygotic twins and 56% in dizygotic twins (p=0.027, Fisher). Conclusions: The results demonstrate that in healthy subjects 46 y of age or younger, the presence of 10 or more hard drusen per eye is highly influenced by hereditary factors. Although large numbers of hard drusen have been shown to predict the development of soft drusen in elderly people, the significance of small hard drusen found in younger subjects with normal visual function remains unknown.

Keywords: age–related macular degeneration • drusen • genetics