title: Heritability of macular pigment: a twin study.
abstract: OBJECTIVE
  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 degrees 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.
authors.affiliation: Twin Research and Genetic Epidemiology Unit, The Rayne Institute, St. Thomas' Hospital, London, United Kingdom.
authors.forename: Shiao Hui Melissa
authors.initials: SH
authors.lastname: Liew
authors.forename: Clare E
authors.initials: CE
authors.lastname: Gilbert
authors.forename: Tim D
authors.initials: TD
authors.lastname: Spector
authors.forename: John
authors.initials: J
authors.lastname: Mellerio
authors.forename: John
authors.initials: J
authors.lastname: Marshall
authors.forename: Fredericus J
authors.initials: FJ
authors.lastname: van Kuijk
authors.forename: Stephen
authors.initials: S
authors.lastname: Beatty
authors.forename: Fred
authors.initials: F
authors.lastname: Fitzke
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Hammond
mesh_terms: D000293:Adolescent; D000328:Adult; D005260:Female; D005453:Fluorescence; D006801:Humans; D007223:Infant; D040582:Inheritance Patterns; D014975:Lutein / Q000235:genetics*; D008875:Middle Aged; D009887:Ophthalmoscopy / Q000379:methods; D010783:Photometry / Q000379:methods; D012168:Retinal Pigments / Q000235:genetics*; D014429:Twins, Dizygotic; D014430:Twins, Monozygotic; D024341:Xanthophylls; D065146:Zeaxanthins; D019207:beta Carotene / Q000031:analogs & derivatives* / Q000235:genetics
chemical_list: D012168:Retinal Pigments; D024341:Xanthophylls; D065146:Zeaxanthins; D019207:beta Carotene; D014975:Lutein