title: Estimation of heritability in myopic twin studies.
abstract: OBJECTIVE
  To examine the genetic and environmental factors for myopia at the family level, as well as risk factors such as ocular measurements and environmental covariates at the individual level, by analysis of myopic twin data.
  
  
  METHODS
  A myopic twin study was conducted on participants from the 2000 Guinness World Records for twins in Taiwan. A total of 130 participants comprising 58 twin pairs and 13 siblings were recruited. The generalized estimating equation approach was used to evaluate the covariate effects. A Bayesian linear mixed model was then used to estimate the heritability.
  
  
  RESULTS
  Pearson's intrapairwise correlation coefficients for ocular refraction and its components were higher among monozygotic twins than among dizygotic twins. The significance of sex suggested that women are more myopic than men. Both axial length and anterior chamber depth were significant factors associated with myopia. The results also showed that people with higher education levels were more likely to have a higher degree of myopia. After accounting for genetic and environmental effects and other covariates, the estimate of heritability of myopia was as high as 0.306.
  
  
  CONCLUSIONS
  After adjusting for environmental covariates, heritability still plays a decisive genetic role in the development of myopia.
authors.affiliation: Institute of Statistics and Information Science, National Changhua University of Education, Chang-Hua, Taiwan.
authors.forename: Miao-Yu
authors.initials: MY
authors.lastname: Tsai
authors.affiliation: Department of Ophthalmology, National Taiwan University Hospital, College of Medicine, National Taiwan University, Taipei, Taiwan.
authors.forename: Luke L-K
authors.initials: LL
authors.lastname: Lin
authors.affiliation: Department of Health, Center for Disease Control and Prevention, Macau, China.
authors.forename: Vicky
authors.initials: V
authors.lastname: Lee
authors.affiliation: Genomic Research Center, Academia Sinica, Taipei, Taiwan.
authors.forename: Chien-Jen
authors.initials: CJ
authors.lastname: Chen
authors.affiliation: Department of Ophthalmology, National Taiwan University Hospital, College of Medicine, National Taiwan University, Taipei, Taiwan. yfshih@ntu.edu.tw.|Department of Ophthalmology, National Taiwan University Hospital, No. 7, Chung Shan South Road, Taipei, 100, Taiwan. yfshih@ntu.edu.tw.
authors.forename: Yung-Feng
authors.initials: YF
authors.lastname: Shih
mesh_terms: D000328:Adult; D004200:Diseases in Twins / Q000235:genetics*; D004522:Educational Status; D004777:Environment; D005260:Female; D006801:Humans; D008297:Male; D009216:Myopia / Q000235:genetics*; D012307:Risk Factors; D014429:Twins, Dizygotic; D014430:Twins, Monozygotic