Heredity of small hard drusen in twins aged 20-46 years

PURPOSE. To examine the prevalence and heredity of small hard drusen in 220 healthy twins aged 20 - 46 years. METHODS. Grayscale digital fundus photography, four-field 50 degrees nonstereoscopic, in red-free illumination was performed in 58 pairs of monozygotic (MZ) twins and 52 pairs of dizygotic (DZ) twins as part of a detailed biometric characterization. Small hard drusen (diameters, < 63 mu m) were counted and graded by distribution type. RESULTS. Small hard drusen were present in 212 of the 220 subjects. Five or more drusen per eye were found in 89 subjects, in three patterns of distribution: scattered drusen (66 subjects), macular drusen (18 subjects), and stippled, innumerable drusen (5 subjects). When analyzed as a continuous trait, the heritability of small hard drusen was 63% (95% confidence interval [CI], 43% to 77%). More than 20 drusen per eye were found in 26 subjects, and the heritability of this phenotype was 99% (95% CI, 82% to 100%). CONCLUSIONS. Hard drusen are prevalent in young adults, and having more than 20 drusen per eye is a highly hereditary feature. Additional research is needed to determine whether the presence of small hard drusen correlates with the development of age-related macular degeneration later in life and to explore the relation to AMD genotypes.