title: The heritability of the ring-like distribution of macular pigment assessed in a twin study.
abstract: OBJECTIVE
  It has been suggested that ring-like patterns of macular pigment, as measured with dual wavelength autofluorescence, are observed less frequently in subjects with age-related maculopathy. We explored relative contributions of genetic and environmental factors in macular pigment optical density (MPOD) distributions using a classic twin study.
  
  
  METHODS
  As part of a previous nutritional study, 322 healthy Caucasian female twins, aged 16 to 50 (mean 40) years, underwent measurement of MPOD optical density by two-wavelength fundus autofluorescence. In the present study, the right eye MPOD profile was assessed for the presence of a ring-like pattern by two graders independently, using common criteria, with a third grader arbitrating in cases of disagreement. Concordance was calculated as 2C/(2C + D), where C is the number of twin pairs concordant, and D the number discordant, for the ring-like pattern. Also, heritability was calculated using maximum-likelihood structural equation modeling.
  
  
  RESULTS
  Images and zygosity data were available for 314 twins (88 monozygotic [MZ] and 69 dizygotic [DZ] pairs). The overall prevalence of the ring pattern was 25.8%. Respective concordances for MZ and DZ twins were 0.75 and 0.22. Additive genetic factors were estimated to contribute to 84.0% of the total variance (95% confidence intervals, 63.7%-94.6%).
  
  
  CONCLUSIONS
  Concordance for MZ twins was over three times that for DZ twins, with heritability estimated at 84%, indicating that genetic factors contribute to the development of the ring structure. Studies have suggested that ring-like patterns of macular pigment can affect risk for age-related maculopathy. In a classic twin study, we found that the presence of such a pattern was highly heritable.
authors.affiliation: Department of Ophthalmology, King's College London, St. Thomas' Hospital Campus, London, United Kingdom.
authors.forename: Ambreen
authors.initials: A
authors.lastname: Tariq
authors.forename: Omar A
authors.initials: OA
authors.lastname: Mahroo
authors.forename: Katie M
authors.initials: KM
authors.lastname: Williams
authors.forename: S H Melissa
authors.initials: SH
authors.lastname: Liew
authors.forename: Stephen
authors.initials: S
authors.lastname: Beatty
authors.forename: Clare E
authors.initials: CE
authors.lastname: Gilbert
authors.forename: Frederik J
authors.initials: FJ
authors.lastname: Van Kuijk
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Hammond
mesh_terms: D000293:Adolescent; D000328:Adult; D002452:Cell Count; D004200:Diseases in Twins / Q000235:genetics*; D005260:Female; D020022:Genetic Predisposition to Disease; D006801:Humans; D008266:Macula Lutea / Q000473:pathology*; D008268:Macular Degeneration / Q000235:genetics* / Q000473:pathology; D009887:Ophthalmoscopy; D012016:Reference Values; D055213:Retinal Pigment Epithelium / Q000473:pathology*; D055815:Young Adult
keywords: heritability; lutein; macular pigment