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Thread: Importance of Genetic Effects for Characteristics of the Human Iris

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    Importance of Genetic Effects for Characteristics of the Human Iris

    Importance of genetic effects for characteristics of the human iris.

    Larsson M, Pedersen NL, Stattin H.

    Department of Behavioral, Social and Legal Sciences, Center for Developmental Research, Orebro University, Sweden. mats.larsson@bsr.oru.se

    The relative importance of genetic influences (heritability) on five general textural quality characteristics of the human iris was assessed using sex and age limitation models. Colour photographs of irises were available from 100 monozygotic twin pairs, 99 dizygotic twin pairs, and 99 unrelated randomly paired age-matched German subjects. Comparative scales were constructed and two judges who were blind to zygosity independently rated five characteristic of the subjects' left iris. Inter-rater reliabilities were larger than.90 for all five scales. The heritabilities for the five iris characteristics ranged from.51-.90. No sex-specific genetic factors were found for the iris characteristics. Age-group differences in heritability were found for one of the five iris characteristics - "distinction of white dot rings". Heritability was greater for the older cohort (90%) than the younger (73%). The iris characteristics that showed the next highest additive-genetic effect were "contractional furrows" (78%) and "frequency of crypts" in the main stroma leaf (66%).

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    Iris colour, ethnic origin and progression of age-related macular degeneration.

    Nicolas CM, Robman LD, Tikellis G, Dimitrov PN, Dowrick A, Guymer RH, McCarty CA.

    Centre for Eye Research Australia, Department of Ophthalmology, University of Melbourne, Melbourne, Victoria, Australia and Marshfield Medical Research Foundation, Marshfield, Wisconsin, USA.

    Aim: To investigate the relationship between iris colour, ethnic origin and the progression of age-related macular degeneration (AMD). Methods: Participants were recruited from the population-based Melbourne Visual Impairment Project or the prospective, randomized, double-masked Vitamin E, Cataract and Age-Related Macular Degeneration study. From these two cohorts, 171 participants aged between 52 and 93 years who were identified as having early AMD features at their baseline examination (1992-1995) were followed for an average of 6.8 years (until 2001) to determine the progression rate of early AMD. The participants' iris colour was categorized as light, intermediate or dark. Ethnic origin was categorized as Anglo-Saxon or non-Anglo-Saxon, according to the participants' grandparents' country of birth. Results: In total, 53 (31%) of the 171 participants showed signs of AMD progression. Participants with light iris colour had twofold the risk of AMD progression of those with dark or intermediate iris colours, although the age-adjusted and multivariate-adjusted associations were not significant (both P = 0.13). Age-adjusted and multivariate comparisons of Anglo-Saxon ethnic origin to non-Anglo-Saxon ethnic origin showed a noticeable but non-significant association with progression of AMD (P= 0.22 and P= 0.14, respectively). Conclusion: Individuals with light iris colour or of Anglo-Saxon ethnic origin had a strong tendency to greater progression of AMD. A larger sample is required to confirm these clinically important, but statistically non-significant, associations.

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