Heritability of central corneal thickness in Chinese: the Guangzhou Twin Eye Study.

PURPOSE To assess the heritability of central corneal thickness (CCT) in Chinese children in a classic twin study. METHODS Twins aged 8 to 16 years were recruited from the Guangzhou Twin Registry. Pachymetry data were obtained by one operator using the same imaging system. Zygosity was confirmed by genotyping with 16 polymorphic markers in all same-sex twin pairs. The CCT of the right eyes was chosen as the trait of interest in the analysis. Heritability was assessed by a general sex-limitation model, using Mx software (University of Richmond, Virginia). RESULTS Four hundred forty-nine twin pairs were available for data analyses, including 131 pairs of monozygotic boys (MZM), 44 pairs of dizygotic boys (DZM), 166 pairs of monozygotic girls (MZF), 31 pairs of dizygotic girls (DZF), and 77 pairs of opposite-sex dizygotic (OSDZ) twins. Twin correlations for CCT were 0.90 for MZM, 0.92 for MZF, 0.56 for DZM, 0.61 for DZF, and 0.44 for OSDZ twins. A sex-limitation model combining additive genetic and unique environmental factors produced the best fit for the data. Heritability estimates for CCT were 0.88 (95% confidence interval [CI]: 0.84-0.91) in the boys and 0.91 (95% CI: 0.89-0.93) in the girls. Unique environmental effects explained only 0.12 (95% CI: 0.09-0.16) and 0.09 (95% CI: 0.07-0.11) of the variance in CCT in the boys and the girls, respectively. CONCLUSIONS Additive genetic effects appear to be the major contributor to the variation of CCT in Chinese population. Heritability of CCT appears to be slightly greater in the girls than in the boys.