Macular Pigment Heritability: A Twin Study

Abstract

Abstract: : Purpose:There is evidence to support the hypothesis that macular pigment (MP) protects against age related macular degeneration however the relative contribution of dietary and genetic factors to the levels of MP is not known. A classical twin study was performed to investigate the relative importance of genes and environment in macular pigment density. Method: Macular pigment optical density (MPOD) was examined in 120 healthy, female twin pairs (64 monozygotic [MZ], 56 dizygotic [DZ]). Subjects were aged between 17 and 50 years (mean age 39.5 years, SD 8.03). MPOD was measured using 2 methods: (1) Heterochromatic flicker photometry (HFP) (2) Fundus autofluorescence (FAF) acquired using a modified HRA at 488nm and 514nm. MPOD for each subject was calculated as the mean MPOD for the two eyes. Univariate maximum likelihood model fitting was used to estimate genetic and environmental variance contributions to MPOD and to determine heritability, the amount of variation explained by genetic effects. Results: MPOD values between each subject’s eyes were highly correlated using both methods (r= 0.76 HFP, 0.96 FAF). Mean MPOD using HFP was 0.43 (SD 0.20). Mean MPOD measured using FAF was 0.28 (SD 0.10). Using both HFP and FAF values, MPOD had a greater correlation within MZ pairs compared to DZ pairs (HFP:MZ r=0.66, DZ= 0.17; FAF MZ r=0.83, DZ= 0.47 ) suggesting a genetic influence on MPOD. Genetic modelling resulted in a best fitting model that involved additive genetic and individual environmental effects. The heritability of MPOD was 0.64 (95% CI 0.46–0.76) for the HFP method and 0.84 (95% CI 0.77–0.90) for FAF method. The rest of the variation was attributable to unique environment (0.36 [0.24–0.54] and 0.16 [0.10–0.23] respectively) Conclusions: Genetic factors play an important role in macular pigment density, with an estimated heritability of 0.64 and 0.84, using HFP and FAF methods respectively. Future studies will provide further insight into the possible mechanisms in which genes may influence the amount of macular pigment.

Keywords: macular pigment • age-related macular degeneration • nutritional factors