Genetics in Glaucoma patients of African descent study (GIGA): Genetic African ancestry is associated with central corneal thickness and intraocular pressure in primary open-angle glaucoma patients.

Abstract

Purpose : To unravel the relationship between African ancestry, central corneal thickness (CCT), and intraocular pressure (IOP) by estimating the genetic African ancestry(GAA) proportion in primary open-angle glaucoma (POAG) patients and controls from an admixed South African Coloured (SAC) and a South African Black (SAB) population.

Methods : In this case-control study, 254 self-reported SAC and 158 self-reported SAB participants were recruited from an university clinic in Cape Town, South Africa. All participants were genotyped on the Illumina HumanOmniExpress beadchip or HumanOmni2.5Exome beadchip. ADMIXTURE was used to infer participant’s GAA among 86632 SNP’s. Linear and logistic regression models were used to assess the relation between GAA, POAG, CCT and IOP.

Results : The median proportion GAA was 60% (IQR=70.3) in the study population. Participants with a higher proportion GAA presented with a significantly thinner CCT (P<0.001; β= -4.09 µm per 10% increase in GAA). The effect of GAA on CCT was marginally different among POAG patients vs controls (P=0.066). POAG patients with a higher percentage GAA showed a significantly higher IOP (P=0.034, β=0.49 mmHg per 10% increase in GAA). In POAG patients, the CCT was significantly thinner compared to controls after adjusting for age and gender (P=0.016; OR=1.071 per 10 µm decrease in CCT). In a stratified analysis in participants with a greater than the median GAA, we did not observe any association with CCT and POAG (P=0.550; OR=1.030 per 10 µm decrease in CCT).

Conclusions : This study demonstrated that a higher proportion of GAA was associated with a thinner CCT and a higher IOP in POAG patients. Regardless of genetic ethnicity, a thinner CCT was associated with POAG when adjusted for gender and age. Remarkably, at higher proportions of GAA, the difference in CCT between POAG and controls was reduced. A stratified analysis showed that the association between CCT and POAG was mainly driven by participants with little GAA. This suggests that a thinner CCT is not associated with POAG in Africans and that assessing the CCT in Sub-Saharan Africans may not be of significantly added value in POAG screening.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.