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Zoe A. Forkin, Pirro G. Hysi, Samantha J. Fahy, Diana P. Kozareva, Christopher J. Hammond; The Effects of Genetics, Environment and Age on 10 Year Progression of Nuclear Cataracts: A Twin Study. Invest. Ophthalmol. Vis. Sci. 2012;53(14):2296.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate the effects of genetic and environmental factors on the progression of nuclear cataract using a twin model.
Nuclear cataract was measured in 325 subjects in 1998-99 and again in 2006-10 using a highly quantitative measure of the nucleus density from digital Scheimpflug images. This included 161 pairs of white female twins (76 monozygotic and 85 dizygotic pairs) aged between 58 and 83 years (mean 69.8) at their second visit. The mean follow up time was 9.4 years (range 7-12 years).EPIC food frequency questionnaires were performed at the baseline visit and nutrient intake was calculated. Change in nuclear cataract was regressed, using forward step-wise linear regression. Structural equation modelling using the Mx program determined the relative contributions of genetic and environmental factors in cataract progression.
The results were highly affected by age. There was no heritability of cataract progression in those under 70 years (n=174), the best fitting model explaining variance by shared (8%) and individual (92%) environmental factors. In contrast the heritability in those above 70 years (n=151) was 0.82 (95% CI, 0.62-0.91) and individual environment explained only 18% (95% CI, 9-38%) of the variance.In the younger subjects, nuclear cataract progression was associated with total energy (kcal) intake (β=4x10-3 95% CI, 1x10-3 to 7x10-3, p=0.01) and dietary Vitamin C (mg) intake had a protective effect (β=-0.04 95% CI, -0.06 to -0.011, p=0.005) but neither were significant in the older subjects (p>0.1).When analysing the cohort as whole, the effects of total energy and Vitamin C intake were significant (p=0.026, p=0.035). The best fitting model estimated genetic factors explain 34% (95% CI, 11-52%) of variance and individual environmental factors account for the remaining 66% (95% CI, 47-88%).
The relative effects of genetic and environmental factors appear to vary highly depending on the age of the subject. Progression of cataract over almost 10 years is largely due to environmental factors in people under 70. Our data confirms a protective effect of dietary Vitamin C and suggests high energy intake increases risk in this population. In those over 70 years, the influence is largely from genetic factors, with environment having little effect on cataract progression.
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