Genetic and environmental contributions to the variance of the Belin-Ambrósio Enhanced Ectasia Display "D" score explored in a classic twin study

Abstract

Purpose : The Belin-Ambrósio Enhanced Ectasia Display "D" (BAD-D) score is a summary corneal tomographic parameter shown to be sensitive in detecting subclinical keratoconus. We explored heritability of this parameter in a largely healthy twin cohort.

Methods : Scheimpflug corneal imaging was performed using the Oculus HR (High-Resolution) Pentacam (Oculus, Wetzlar, Germany) in adult volunteers recruited from the TwinsUK registry based at St Thomas' Hospital in London. Images from the right eye were used for analysis. Only complete twin pairs were included. The BAD-D parameter was noted, and coefficients of intra-pair correlation were calculated for monozygotic (MZ) and dizygotic (DZ) twin pairs. Heritability was estimated by maximum likelihood structural equation modelling using the OpenMx package.

Results : Images from 136 twin volunteers (37 MZ and 31 DZ pairs) were included. Mean (SD) age was 61 (11) years. The majority (93%) were female, reflecting the demographics of the registry. The mean (SD) value of the BAD-D parameter was 1.27 (0.73). Tests of normality did not detect significant deviation from a normal distribution. Pearson coefficients of intra-pair correlation were 0.68 (p = 4.1 x 10^-6) and 0.33 (p = 0.066) for MZ and DZ pairs respectively. The age-adjusted estimate of heritability was 66.4% (95% CI, 46.6-79.2).

Conclusions : The calculated intra-pair correlation coefficient for MZ twins was double that for DZ twins, indicating that the majority of the variance in this parameter is determined by genetic factors. We estimated that approximately two thirds of the variance was attributable to genetic factors. Further studies can seek to identify associated genes.

This is a 2021 ARVO Annual Meeting abstract.