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P.R. Healey, A.J. Lee, P. Mitchell, C.E. Gilbert, T.D. Spector, C.J. Hammond; The Genetic Basis of Peripapillary Atrophy: The Twin Eye Study . Invest. Ophthalmol. Vis. Sci. 2004;45(13):4395.
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Purpose:Peripapillary atrophy (PPA) is a relatively common optic disc finding strongly associated with both prevalence and progression of open–angle glaucoma (OAG). While a genetic basis for OAG is well described, the heritability of PPA or its relationship to environmental factors is unknown. This study aimed to analyze the relative strengths of dominant and additive inheritance, common environment and unique environment on PPA. Methods:506 pairs of female twins (226 monozygotic and 280 dizygotic) aged 49 to 79 years (mean 62 years) were recruited from the St Thomas' UK Adult Twin Registry. Examination included 30–degree non–simultaneous stereoscopic photographs taken with a Kowa camera using Kodak Ektachrome 64 film. Photographs were examined stereoscopically and the best stereo–pair was digitized. Masked optic disc grading identified PPA (types alpha and beta) based the descriptions by Jonas and the protocols from the Blue Mountains Eye Study. Multivariate structural equation modeling was performed using Mx and tetrachoric correlations with asymptotic covariance matrices derived from PRELIS. Results:Optic disc photographs could be graded for right eyes of both subjects in 179 MZ twin pairs and 229 DZ twin pairs, with an overall beta–PPA prevalence of 23% (SE 1.7%). The case–wise concordance for beta–PPA in right eyes was 0.60 (95% CI 0.47–0.74) for MZ pairs and 0.39 (95% CI 0.28–0.50) for DZ pairs (p difference=0.02), with an MZ/DZ risk ratio of 1.55. Data for left eyes gave similar findings. Multivariate modeling, adjusting for age and spherical equivalent, resulted in a best–fit model involving additive genetic effects and individual environment, with no shared environment or dominant genetic effect. The heritability of beta–PPA in this sample was 0.80 (95% CI 0.74–0.85), and spherical equivalent 0.84 (95% CI 0.79–0.90); age had no significant effect on the variance. The genetic correlation between beta–PPA and spherical equivalent was –0.37, confirming the link between myopia (negative spherical equivalent) and presence of beta–PPA. Conclusions:The presence of beta–PPA, a frequent ocular finding known to be associated with open–angle glaucoma, appears to be under strong genetic control, with some of this genetic effect shared with genes involved in myopia.
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