Purpose: To estimate the extent to which common genetic and environmental effects contribute to covariances among axial length, anterior chamber depth, and angle-opening distance.
Methods: The study participants were recruited from the Guangzhou Twin Registry. Anterior segment optical coherence tomography and custom software were used to quantify the angle opening distance (AOD) at the location 500 microm anterior to the scleral spur. Anterior chamber depth (ACD) and axial length (AL) were measured using laser interferometry. Cross-trait, cross-twin correlations for monozygotic (MZ) and dizygotic (DZ) twins and the Cholesky model were used to quantify shared genetic and environmental effects for AL, ACD, and AOD after adjusting for age and sex.
Results: A group of 459 pairs of twins (304 MZ and 155 DZ) aged 8 to 16 years were available for analysis. The phenotypic correlations among AL, ACD, and AOD ranged from 0.39 to 0.64. Cross-twin, cross-trait correlations for these three phenotypes for MZ twins were consistently greater than the corresponding correlations for DZ twins. The results of the Cholesky model-fitting analyses can be summarized as follows: first, of 70% of additive genetic factors for AOD, 23% and 13% were those shared with ACD and AL, respectively, whereas the remaining 34% were those unique to AOD. Second, of 89% of additive genetic factors for ACD, 25% were those shared with AL, whereas 64% were those unique to ACD. Third, random environmental influences on covariances among AL, ACD, and AOD were very small.
Conclusions: Analyses of Chinese children twin data suggest that shared genes are responsible for the significant phenotypic correlations found for AL ACD, and AOD.