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Heritability of Macular Pigment: A Twin Study

¹From the Twin Research and Genetic Epidemiology Unit and the ⁴Department of Ophthalmology, The Rayne Institute, St. Thomas’ Hospital, London, United Kingdom; the ²International Centre for Eye Health, London School of Hygiene and Tropical Medicine, University of London, London, United Kingdom; the ³School of Biosciences, University of Westminster, London, United Kingdom; the ⁵Department of Ophthalmology and Visual Sciences, University of Texas Medical Branch, Galveston, Texas; the ⁶Department of Chemical and Life Sciences, Waterford Institute of Technology, Waterford, Ireland; the ⁷Institute of Ophthalmology, London, United Kingdom; and the ⁸Princess Royal University Hospital, Bromley Hospitals NHS Trust, Orpington, United Kindgom.

PURPOSE. Several studies have reported higher levels of macular pigment (MP) in association with reduced risk for age-related macular degeneration (ARMD), a disease to which there is a genetic predisposition. A classic twin study was performed to determine the heritability of MP in the healthy eye.

METHODS. One hundred fifty twin pairs (76 monozygotic [MZ] and 74 dizygotic [DZ]), aged 18 to 50 years, participated. MP optical density was measured psychophysically with heterochromatic flicker photometry (HFP) and also with an imaging method involving fundus autofluorescence (AF). The covariance of MP within MZ and DZ twin pairs was compared, and genetic modeling techniques were used to determine the relative contributions of genes and environment to the variation in MP.

RESULTS. The mean MP optical density, measured using HFP, was 0.43 ± 0.21. Using AF, the mean MP optical density, measured at 1° eccentricity, was 0.28 ± 0.11. MP optical densities correlated more highly in MZ twins than in DZ twins, according to both HFP (MZ: 0.65; DZ: 0.24) and AF (MZ: 0.83; DZ: 0.50). A model combining additive genetic and unique environmental effects provided the best fit and resulted in MP heritability estimates of 0.67 (95% CI, 0.52–0.77) and 0.85 (95% CI, 0.78–0.90) for HFP and AF readings, respectively.

CONCLUSIONS. This classic twin study demonstrates that genetic background is an important determinant of MP optical density, reflected in heritability estimates of 0.67 and 0.85 for HFP and AF measures, respectively.

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