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N. C. Taarnhoj, L. Kessel, B. Sander, J. L. Hougaard, T. I. A. Sørensen, M. Larsen; Heritability of Retinal Vessel Tortuosity - A Twin Study. Invest. Ophthalmol. Vis. Sci. 2007;48(13):4161.
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© ARVO (1962-2015); The Authors (2016-present)
To assess the relative contributions of genetic and environmental effects on retinal vessel tortuosity.
Understanding the genetic and environmental influence on the layout of retinal blood vessels may facilitate elucidation of the pathogenesis of disease in the human retina. We conducted a cross-sectional study of 58 monozygotic and 52 dizygotic same-sex healthy twin pairs, aged 20 to 46 y, recruited from The Danish Twin Registry. Tortuosity was assessed by visual grading of digital fundus photographs (60 degree, 1024x1024 pixels) of right and left eyes by two independent graders. Retinal arteries were graded on a scale from 1 to 3, in order of increasing tortuosity. The variation in venous tortuosity was small and consequently, we abstained from grading the parameter. The classical twin model is based on the assumption that MZ twins have identical genotypes, for which reason all observed differences between the two twins in a pair are attributable to environmental factors. DZ twins, however, share on average 50% of their genes. The extent to which MZ twins are more alike than DZ twins is therefore assumed to reflect a genetic influence on the phenotype in question. Pearson correlations, probandwise and pairwise concordance rates were calculated.
The Pearson correlation between twin A and twin B was higher for monozygotic twin pairs, (0.55) than for dizygotic twin pairs (0.42), indicating a minor genetic effect. Structural equation modelling (twin statistics) supported that an AE model was the best fitting model for arteries. Pairwise concordance rates were 79.2% (95% C.I. 70.2, 88.1%) for monozygotic twins and 80.5% (95% C.I. 71.4, 89.6%) for dizygotic twins. Probandwise concordance rates were 65.5% (95% C.I. 53.3, 77.7%) for monozygotic twins and 67.3% (95% C.I. 54.6, 80.1%) for dizygotic twins.
Using Pearson correlations and concordance rates to compare the grade of tortuousity in arteries in a study of healthy monozygotic and dizygotic twins aged 20-46 y, we found no evidence of a significant genetic influence on vessel tortuousity in the retina.
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