title: Heritability of optic disc and cup measured by the Heidelberg Retinal Tomography in Chinese: the Guangzhou twin eye study.
abstract: OBJECTIVE
  To assess the heritability of disc area (DA), cup area (CA), and cup-disc area ratio (CDAR) as intermediate phenotypes for glaucoma in Chinese subjects in a classic twin study.
  
  
  METHODS
  Twins (n = 1160) aged 7 to 15 years were identified in the Guangzhou Twin Registry. Optic disc parameters were measured with a Heidelberg Retina Tomograph (HRT; Heidelberg Engineering GmbH, Heidelberg, Germany) by the same examiner and grader. Zygosity was confirmed by genotyping with 16 polymorphic markers in all same-sex twin pairs. The DA, CA, and CDAR of the right eyes were chosen as the traits of interest in the analysis. Heritability was assessed by structural variance component genetic modeling, with Mx quantitative genetic modeling software, after adjustment for age and gender.
  
  
  RESULTS
  Of those recruited, 1114 twins were identified in the analysis, including 355 monozygotic (MZ) and 202 dizygotic (DZ) twin pairs. The intraclass correlation coefficients were 0.79 for DA, 0.83 for CA, and 0.80 for CDAR in MZ pairs and 0.30, 0.37, and 0.35, respectively, in DZ pairs. The age- and sex-adjusted variance component model identified additive genetic and unshared environmental effects (AE model) being best fit for DA, CA, and CDAR. This best-fitting model yielded 77.3% additive genetic (95%CI: 73.0%-80.8%) and 22.7% unshared environment (95% CI: 19.2%-27.0%) for DA, 82.7% (95% CI:79.4%-85.5%) and 17.3% (95% CI: 14.5%-20.6%) for CA, 78.6% (95% CI: 74.5%-82.0%) and 21.4% (95% CI: 18.0%-25.4%) for CDAR.
  
  
  CONCLUSIONS
  The variance of optic nerve head parameters (DA, CA, and CDAR) appears to be attributable to additive genetic and unshared environmental effects. Approximately 80% of these phenotypic variances are genetically determined.
authors.affiliation: State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, China. mingguang_he@yahoo.com
authors.forename: Mingguang
authors.initials: M
authors.lastname: He
authors.forename: Bin
authors.initials: B
authors.lastname: Liu
authors.forename: Wenyong
authors.initials: W
authors.lastname: Huang
authors.forename: Jian
authors.initials: J
authors.lastname: Zhang
authors.forename: Qiuxia
authors.initials: Q
authors.lastname: Yin
authors.forename: Yingfeng
authors.initials: Y
authors.lastname: Zheng
authors.forename: Dandan
authors.initials: D
authors.lastname: Wang
authors.forename: Jian
authors.initials: J
authors.lastname: Ge
mesh_terms: D000293:Adolescent; D044466:Asian People / Q000235:genetics*; D002648:Child; D002681:China; D005260:Female; D005838:Genotype; D006801:Humans; D040582:Inheritance Patterns; D008297:Male; D009887:Ophthalmoscopy; D009898:Optic Disk / Q000033:anatomy & histology*; D012042:Registries; D014054:Tomography / Q000379:methods; D014429:Twins, Dizygotic / Q000235:genetics*; D014430:Twins, Monozygotic / Q000235:genetics*