Age-related macular degeneration discordance in monozygotic twin pairs

Purpose: To examine age-related macular degeneration (AMD) and retinal pigment epithelium (RPE)-Bruch's membrane (BrM) complex volume associations in monozygotic twin pairs. Methods: In this study, 106 elderly twins (53 twin pairs) from the Finnish Twin Cohort study were recruited. Each participant underwent dilated 35-degree digital colour fundus photography (CFP), and spectral domain optical coherence tomography (OCT) and replied to a structured study questionnaire. The CFPs were graded according to the Age-Related Eye Disease Study (AREDS) classification. The OCT images were segmented and volumetric data of the RPE-BrM complex volume was calculated with the Orion (TM) software. The worse eye according to AREDS classification was used for the analysis. Results: Twenty-nine (55%) of the twin pairs were discordant with regard to AREDS classification. Fourteen (26%) pairs were discordant with one twin participant having AMD (AREDS 2-4) and the other being unaffected (AREDS 1). Four (8%) pairs had one twin participant with intermediate or late AMD (AREDS 3-4) versus the other being unaffected (AREDS 1). The within-pair polychoric correlation for AREDS was 0.605 (95% confidence interval 0.418-0.792). In multivariate analysis intermediate and late AMD as well as age associated with RPE-BrM complex volume. RPE-BrM complex volume showed a within twin pair correlation, r = 0.430 (95% confidence interval 0.172-0.688, p < 0.01). Conclusion: A substantial proportion of monozygotic twin pairs are discordant with regard to age-related macular degeneration phenotype. RPE-BrM complex volume associated with age and intermediate and late AMD.