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M. He, J. Xu, W. Huang, J. Zhang, Y. Zheng; High Heritability of Refractive Error, Corneal Curvature and Axial Length in Chinese School-Aged Children: A Population-based Twin Eye Study in Guangzhou. Invest. Ophthalmol. Vis. Sci. 2007;48(13):2886.
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© ARVO (1962-2015); The Authors (2016-present)
To assess the heritability of refractive error and its related traits corneal curvature and axial length in Chinese using a classic twin study.
Guangzhou Twin Registry was established in 2005. Twins aged 7 to 15 years living in two districts closest to the examination station were recruited from this registry. Refractive error was measured using an autorefractor after cycloplegia. Corneal curvature and axial length were measured using a Zeiss IOLMaster. Subjects with retinopathy of prematurity, congenital cataract and other abnormalities were excluded. Zygosity in all twin pairs was confirmed by genotyping with 16 polymorphic markers. Spherical equivalent (SE), corneal curvature (CC) and axial length (AL) of the right eye were in analysis. Heritability was assessed by structural variance component genetic modeling using Mx software.
Among 867 twin pairs who were invited and successfully contacted, 580 pairs were examined and 563 pairs were available for analysis, which included 359 monozygotic (MZ) and 204 dizygotic (DZ) twin pairs. The mean age of the subjects was 10.8±2.6 years (range 7-15 years). Myopia (SE<-0.5D) was identified in 37.8 % twins, increasing from 8.5% in 7 years to 69.8% in 15 years. The means CC and AL for the cohort were 43.8 ±1.5 diopters and 23.5±1.1 mm. Intraclass correlation coefficients were 0.85 in MZ and 0.40 in DZ twins for SE (P<0.0001), 0.89 and 0.47 for CC (P<0.0001) and 0.90 and 0.45 respectively for AL(P<0.0001). An age-adjusted model identified 80.7 % additive genetic (95%CI:77.0~83.8%) and 19.3% unique environment (95%CI:16.2~23.0%) being best fit for SE, 87.9% additive genetic (95%CI:85.6~89.8%) and 12.1% unique environment (95%CI:10.2~14.4%) for CC, 86.4% % additive genetic (95%CI:83.8~88.6%) and 13.6% unique environment (95%CI:11.4~16.2%) for AL.
Prevalence of myopia in this twin cohort was similar to population singleton data. Myopia is believed to be highly environmentally determined in Asians, however, this twin study evident the high heritability of myopia in Chinese children. More work is needed to accept or refuse the greater similarities in MZ being due to similarities of environmental factors.
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