Genome-wide association and admixture analysis of glaucoma in the Women's Health Initiative

Performance of Polygenic Risk Scores for Primary Open-Angle Glaucoma in Populations of African Descent

Importance

Primary open-angle glaucoma (POAG) polygenic risk scores (PRSs) continue to be evaluated in primarily European-ancestry populations despite higher prevalence and worse outcomes in African-ancestry populations.

Objective

To evaluate how established POAG PRSs perform in African-ancestry samples from the Genetics in Glaucoma Patients of African Descent (GIGA), Genetics of Glaucoma in Individuals of African Descent (GGLAD), and Million Veteran Program (MVP) datasets and compare these with European-ancestry samples.

Design, Setting, and Participants

This was a multicenter, cross-sectional study of POAG cases and controls from Tanzania, South Africa, Nigeria, Ghana, and the US. Included were individuals of African descent from South Africa and Tanzania from the GIGA dataset; individuals of African descent from Ghana, Nigeria, and the US from the GGLAD dataset; and individuals of African or European descent from the US in the MVP dataset. Data were analyzed from January 2022 to July 2023.

Exposures

Three PRSs derived from large meta-analyses of European and Asian populations, namely Gharahkhani et al (Gharahkhani PRS), Han et al (Han PRS), and Craig et al (Craig PRS).

Main Outcomes and Measures

Odds ratios (ORs) for POAG risk stratification comparing the highest and lowest quintiles; area under the receiver operating characteristic curve (AUROC), and liability coefficient of determination (R2) for the addition of PRS to a baseline of age, sex, and first 5 principal components.

Results

A total of 11 673 cases and 66 432 controls were included in this study across 7 ancestral groups. Mean (SD) age of the total participants was 76.9 (8.7) years, with 74 304 males (95.1%). The following were included in each dataset: GIGA (663 cases, 476 controls), GGLAD (1471 cases, 1482 controls), and MVP (9559 cases, 64 474 controls). Increases in ORs were found for the highest POAG risk quintile ranging from an OR of 1.68 (95% CI, 1.17-2.43) in Ghanaians to 7.05 (95% CI, 2.73-19.6) in the South African multiple ancestry group (which derives from at least 5 distinct ancestral groups: Khoisan, Bantus, Europeans, Indians, and Southeast Asians) with the Gharahkhani PRS. The Han PRS showed OR increases for the highest POAG risk quintile ranging from 2.27 (95% CI, 1.49-3.47) in African American individuals in the GGLAD dataset to 7.24 (95% CI, 6.47-8.12) in Europeans. The Craig PRS predicted OR increases in the highest quintile for all groups ranging from 1.51 (95% CI, 1.05-2.18) in Ghanaians to 6.31 (95% CI, 5.67-7.04) in Europeans. However, AUROC and R2 increases above baseline were lower for all African-ancestry compared with European-ancestry groups in the 3 tested PRSs.

Conclusions and Relevance

In this cross-sectional study, despite some improvements in OR-based risk stratification using the Gharahkhani PRSs, Han PRSs, and Craig PRSs, consistently lower improvements in AUROC and R2 for African-ancestry compared with European-ancestry groups highlight the need for risk prediction models tailored to diverse populations.

A multi-cohort genome-wide association study in African ancestry individuals reveals risk loci for primary open-angle glaucoma

Primary open-angle glaucoma (POAG), the leading cause of irreversible blindness worldwide, disproportionately affects individuals of African ancestry. We conducted a genome-wide association study (GWAS) for POAG in 11,275 individuals of African ancestry (6,003 cases; 5,272 controls). We detected 46 risk loci associated with POAG at genome-wide significance. Replication and post-GWAS analyses, including functionally informed fine-mapping, multiple trait co-localization, and in silico validation, implicated two previously undescribed variants (rs1666698 mapping to DBF4P2; rs34957764 mapping to ROCK1P1) and one previously associated variant (rs11824032 mapping to ARHGEF12) as likely causal. For individuals of African ancestry, a polygenic risk score (PRS) for POAG from our mega-analysis (African ancestry individuals) outperformed a PRS from summary statistics of a much larger GWAS derived from European ancestry individuals. This study quantifies the genetic architecture similarities and differences between African and non-African ancestry populations for this blinding disease.

Paving the way while playing catch up: mitochondrial genetics in African ancestry primary open-angle glaucoma

Glaucoma, the leading cause of irreversible blindness worldwide, disproportionately affects individuals of African descent. Specifically, previous research has indicated that primary open-angle glaucoma (POAG), the most common form of disease, is more prevalent, severe, early-onset, and rapidly-progressive in populations of African ancestry. Recent studies have identified genetic variations that may contribute to the greater burden of disease in this population. In particular, mitochondrial genetics has emerged as a profoundly influential factor in multiple neurodegenerative diseases, including POAG. Several hypotheses explaining the underlying mechanisms of mitochondrial genetic contribution to disease progression have been proposed, including nuclear-mitochondrial gene mismatch. Exploring the fundamentals of mitochondrial genetics and disease pathways within the understudied African ancestry population can lead to groundbreaking advancements in the research and clinical understanding of POAG. This article discusses the currently known involvements of mitochondrial genetic factors in POAG, recent directions of study, and potential future prospects in mitochondrial genetic studies in individuals of African descent.

Diversity in Polygenic Risk of Primary Open-Angle Glaucoma

Glaucoma is the leading cause of irreversible blindness worldwide. Primary open-angle glaucoma (POAG), the most common glaucoma subtype, is more prevalent and severe in individuals of African ancestry. Unfortunately, this ancestral group has been historically under-represented among genetic studies of POAG. Moreover, both genetic and polygenic risk scores (GRS, PRS) that are typically based on genetic data from European-descent populations are not transferable to individuals without a majority of European ancestry. Given the aspirations of leveraging genetic information for precision medicine, GRS and PRS demonstrate clinical potential but fall short, in part due to the lack of diversity in these studies. Prioritizing diversity in the discovery of risk variants will improve the performance and utility of GRS and PRS-derived risk estimation for disease stratification, which could bring about earlier POAG intervention and treatment for a disease that often goes undetected until significant damage has occurred.

Glaucoma Genetic Risk Scores in the Million Veteran Program

PURPOSE

Primary open-angle glaucoma (POAG) is a degenerative eye disease for which early treatment is critical to mitigate visual impairment and irreversible blindness. POAG-associated loci individually confer incremental risk. Genetic risk score(s) (GRS) could enable POAG risk stratification. Despite significantly higher POAG burden among individuals of African ancestry (AFR), GRS are limited in this population. A recent large-scale, multi-ancestry meta-analysis identified 127 POAG-associated loci and calculated cross-ancestry and ancestry-specific effect estimates, including in European ancestry (EUR) and AFR individuals. We assessed the utility of the 127-variant GRS for POAG risk stratification in EUR and AFR Veterans in the Million Veteran Program (MVP). We also explored the association between GRS and documented invasive glaucoma surgery (IGS).

DESIGN

Cross-sectional study.

PARTICIPANTS

MVP Veterans with imputed genetic data, including 5830 POAG cases (445 with IGS documented in the electronic health record) and 64 476 controls.

METHODS

We tested unweighted and weighted GRS of 127 published risk variants in EUR (3382 cases and 58 811 controls) and AFR (2448 cases and 5665 controls) Veterans in the MVP. Weighted GRS were calculated using effect estimates from the most recently published report of cross-ancestry and ancestry-specific meta-analyses. We also evaluated GRS in POAG cases with documented IGS.

MAIN OUTCOME MEASURES

Performance of 127-variant GRS in EUR and AFR Veterans for POAG risk stratification and association with documented IGS.

RESULTS

GRS were significantly associated with POAG (P < 5 × 10-5) in both groups; a higher proportion of EUR compared with AFR were consistently categorized in the top GRS decile (21.9%-23.6% and 12.9%-14.5%, respectively). Only GRS weighted by ancestry-specific effect estimates were associated with IGS documentation in AFR cases; all GRS types were associated with IGS in EUR cases.

CONCLUSIONS

Varied performance of the GRS for POAG risk stratification and documented IGS association in EUR and AFR Veterans highlights (1) the complex risk architecture of POAG, (2) the importance of diverse representation in genomics studies that inform GRS construction and evaluation, and (3) the necessity of expanding diverse POAG-related genomic data so that GRS can equitably aid in screening individuals at high risk of POAG and who may require more aggressive treatment.

Learning from Black/African American Participants: Applying the Integrated Behavioral Model to Assess Recruitment Strategies for a Glaucoma Genetic Study

The underrepresentation of African American (AA) participants in medical research perpetuates racial health disparities in the United States. Open-ended phone interviews were conducted with 50 AA adults from Philadelphia who had previously participated in a genetic study of glaucoma that included complimentary ophthalmic screenings. Recruitment for the genetic study was done in partnership with a Black-owned radio station. Thematic analysis of interview transcripts, guided by the integrated behavior model (IBM), identified self-reported motivations for participating in this care-focused and community-promoted research program. Findings revealed that decisions to enroll were influenced by strong instrumental attitudes regarding learning more about personal health and contributing to future care options for others. Notable normative influences that factored into participants' decisions to enroll in the study included hearing about the study from a respected community media outlet, friends, and family. About one-third of respondents discussed past and current racial discrimination in medical research as an important sociocultural frame within which they thought about participation, suggesting that experiential attitudes play a continuing role in AA's decisions to enroll in medical research studies. Medical researchers seeking to recruit AA participants should collaborate with community partners, combine enrollment opportunities with access to health services, and emphasize the potential for new research to mitigate racial inequalities.

Association of the SNP rs112369934 near TRIM66 Gene with POAG Endophenotypes in African Americans

We investigated the association of the single nucleotide polymorphism (SNP) rs112369934 near the TRIM66 gene with qualitative and quantitative phenotypes of primary open-angle glaucoma (POAG) in African Americans (AA). AA subjects over 35 years old were recruited for the Primary Open-Angle African American Glaucoma Genetics (POAAGG) study in Philadelphia, PA. Glaucoma cases were evaluated for phenotypes associated with POAG pathogenesis, and the associations between rs112369934 and phenotypes were investigated by logistic regression analysis and in gender-stratified case cohorts: The SNP rs112369934 was found to have a suggestive association with retinal nerve fiber layer (RNFL) thickness and cup-to-disc ratio (CDR) in 1087 male AA POAG cases, individuals with the TC genotype having thinner RNFL (95% CI 0.85 to 6.61, p = 0.01) and larger CDR (95% CI -0.07 to -0.01, p = 0.02) than those with wildtype TT. No other significant associations were found. In conclusion SNP rs112369934 may play a role in POAG pathogenesis in male AA individuals. However, this SNP has been implicated in higher POAG risk in both male and female AA POAG cases.

Eyes of Africa: The Genetics of Blindness: Study Design and Methodology

BACKGROUND

This report describes the design and methodology of the "Eyes of Africa: The Genetics of Blindness," a collaborative study funded through the Human Heredity and Health in Africa (H3Africa) program of the National Institute of Health.

METHODS

This is a case control study that is collecting a large well phenotyped data set among glaucoma patients and controls for a genome wide association study. (GWAS). Multiplex families segregating Mendelian forms of early-onset glaucoma will also be collected for exome sequencing.

DISCUSSION

A total of 4500 cases/controls have been recruited into the study at the end of the 3rd funded year of the study. All these participants have been appropriately phenotyped and blood samples have been received from these participants. Recent GWAS of POAG in African individuals demonstrated genome-wide significant association with the APBB2 locus which is an association that is unique to individuals of African ancestry. This study will add to the existing knowledge and understanding of POAG in the African population.

Risk Stratification and Clinical Utility of Polygenic Risk Scores in Ophthalmology

Translational Relevance

Common genetic variants can be used to effectively stratify the risk of disease development and progression and may be used to guide screening, triaging, monitoring, or treatment thresholds.

The Role of Genetic Ancestry as a Risk Factor for Primary Open-angle Glaucoma in African Americans

Purpose

POAG is the leading cause of irreversible blindness in African Americans. In this study, we quantitatively assess the association of autosomal ancestry with POAG risk in a large cohort of self-identified African Americans.

Methods

Subjects recruited to the Primary Open-Angle African American Glaucoma Genetics (POAAGG) study were classified as glaucoma cases or controls by fellowship-trained glaucoma specialists. POAAGG subjects were genotyped using the MEGA Ex array (discovery cohort, n = 3830; replication cohort, n = 2135). Population structure was interrogated using principal component analysis in the context of the 1000 Genomes Project superpopulations.

Results

The majority of POAAGG samples lie on an axis between African and European superpopulations, with great variation in admixture. Cases had a significantly lower mean value of the ancestral component q0 than controls for both cohorts (P = 6.14-4; P = 3-6), consistent with higher degree of African ancestry. Among POAG cases, higher African ancestry was also associated with thinner central corneal thickness (P = 2-4). Admixture mapping showed that local genetic ancestry was not a significant risk factor for POAG. A polygenic risk score, comprised of 23 glaucoma-associated single nucleotide polymorphisms from the NHGRI-EBI genome-wide association study catalog, was significant in both cohorts (P < 0.001), suggesting that both known POAG single nucleotide polymorphisms and an omnigenic ancestry effect influence POAG risk.

Conclusions

In sum, the POAAGG study population is very admixed, with a higher degree of African ancestry associated with an increased POAG risk. Further analyses should consider social and environmental factors as possible confounding factors for disease predisposition.

Evaluation of a multimedia marketing campaign to engage African American patients in glaucoma screening

Our objective was to determine which messaging approaches from a marketing campaign were most effective in recruiting African American individuals to a glaucoma screening and research study. We conducted a multimedia marketing campaign in Philadelphia from 01/31/2018 to 06/30/2018. Messaging approaches included radio advertisements and interviews (conducted in partnership with a local radio station with a large African American listener base), print materials, event tables, and online postings. Participants received free glaucoma screenings and the opportunity to enroll in our glaucoma genetics study. These screenings allowed individuals with glaucoma to receive a full examination and treatment plan with a glaucoma specialist, as well as to contribute to future efforts to identify genetic variants underlying this disease. We compared inquiry, enrollment, and cost yield for each messaging approach. Our campaign resulted in 154 unique inquiries, with 98 patients receiving glaucoma screenings (64%) and 60 patients enrolling in our study (39%). Commercials on WURD radio yielded the highest number of inquiries (62%) and enrollments (62%), but at relatively high cost ($814/enrolled patient). The most inexpensive approach that yielded more than five enrollments was postcards ($429/enrolled patient). Our campaign suggests that high-frequency commercials and postcards distributed at targeted healthcare locations are particularly effective and affordable options for connecting with the African American community. Our findings can help to inform recruitment efforts for other understudied diseases in minority populations.

Clinical implications of recent advances in primary open-angle glaucoma genetics

Over the last decade, genetic studies, including genome-wide association studies (GWAS), have accelerated the discovery of genes and genomic regions contributing to primary open-angle glaucoma (POAG), a leading cause of irreversible vision loss. Here, we review the findings of genetic studies of POAG published in English prior to September 2019. In total, 74 genomic regions have been associated at a genome-wide level of significance with POAG susceptibility. Recent POAG GWAS provide not only insight into global and ethnic-specific genetic risk factors for POAG susceptibility across populations of diverse ancestry, but also important functional insights underlying biological mechanisms of glaucoma pathogenesis. In this review, we also summarize the genetic overlap between POAG, glaucoma endophenotypes, such as intraocular pressure and vertical cup-disc ratio (VCDR), and other eye disorders. We also discuss approaches recently developed to increase power for POAG locus discovery and to predict POAG risk. Finally, we discuss the recent development of POAG gene-based therapies and future strategies to treat glaucoma effectively. Understanding the genetic architecture of POAG is essential for an earlier diagnosis of this common eye disorder, predictive testing of at-risk patients, and design of gene-based targeted medical therapies none of which are currently available.

Association of Genetic Variants With Primary Open-Angle Glaucoma Among Individuals With African Ancestry

Importance

Primary open-angle glaucoma presents with increased prevalence and a higher degree of clinical severity in populations of African ancestry compared with European or Asian ancestry. Despite this, individuals of African ancestry remain understudied in genomic research for blinding disorders.

Objectives

To perform a genome-wide association study (GWAS) of African ancestry populations and evaluate potential mechanisms of pathogenesis for loci associated with primary open-angle glaucoma.

Design, Settings, and Participants

A 2-stage GWAS with a discovery data set of 2320 individuals with primary open-angle glaucoma and 2121 control individuals without primary open-angle glaucoma. The validation stage included an additional 6937 affected individuals and 14 917 unaffected individuals using multicenter clinic- and population-based participant recruitment approaches. Study participants were recruited from Ghana, Nigeria, South Africa, the United States, Tanzania, Britain, Cameroon, Saudi Arabia, Brazil, the Democratic Republic of the Congo, Morocco, Peru, and Mali from 2003 to 2018. Individuals with primary open-angle glaucoma had open iridocorneal angles and displayed glaucomatous optic neuropathy with visual field defects. Elevated intraocular pressure was not included in the case definition. Control individuals had no elevated intraocular pressure and no signs of glaucoma.

Exposures

Genetic variants associated with primary open-angle glaucoma.

Main Outcomes and Measures

Presence of primary open-angle glaucoma. Genome-wide significance was defined as P < 5 × 10-8 in the discovery stage and in the meta-analysis of combined discovery and validation data.

Results

A total of 2320 individuals with primary open-angle glaucoma (mean [interquartile range] age, 64.6 [56-74] years; 1055 [45.5%] women) and 2121 individuals without primary open-angle glaucoma (mean [interquartile range] age, 63.4 [55-71] years; 1025 [48.3%] women) were included in the discovery GWAS. The GWAS discovery meta-analysis demonstrated association of variants at amyloid-β A4 precursor protein-binding family B member 2 (APBB2; chromosome 4, rs59892895T>C) with primary open-angle glaucoma (odds ratio [OR], 1.32 [95% CI, 1.20-1.46]; P = 2 × 10-8). The association was validated in an analysis of an additional 6937 affected individuals and 14 917 unaffected individuals (OR, 1.15 [95% CI, 1.09-1.21]; P < .001). Each copy of the rs59892895*C risk allele was associated with increased risk of primary open-angle glaucoma when all data were included in a meta-analysis (OR, 1.19 [95% CI, 1.14-1.25]; P = 4 × 10-13). The rs59892895*C risk allele was present at appreciable frequency only in African ancestry populations. In contrast, the rs59892895*C risk allele had a frequency of less than 0.1% in individuals of European or Asian ancestry.

Conclusions and Relevance

In this genome-wide association study, variants at the APBB2 locus demonstrated differential association with primary open-angle glaucoma by ancestry. If validated in additional populations this finding may have implications for risk assessment and therapeutic strategies.

Genome-wide association study of primary open-angle glaucoma in continental and admixed African populations

Primary open angle glaucoma (POAG) is a complex disease with a major genetic contribution. Its prevalence varies greatly among ethnic groups, and is up to five times more frequent in black African populations compared to Europeans. So far, worldwide efforts to elucidate the genetic complexity of POAG in African populations has been limited. We conducted a genome-wide association study in 1113 POAG cases and 1826 controls from Tanzanian, South African and African American study samples. Apart from confirming evidence of association at TXNRD2 (rs16984299; OR[T] 1.20; P = 0.003), we found that a genetic risk score combining the effects of the 15 previously reported POAG loci was significantly associated with POAG in our samples (OR 1.56; 95% CI 1.26-1.93; P = 4.79 × 10-5). By genome-wide association testing we identified a novel candidate locus, rs141186647, harboring EXOC4 (OR[A] 0.48; P = 3.75 × 10-8), a gene transcribing a component of the exocyst complex involved in vesicle transport. The low frequency and high degree of genetic heterogeneity at this region hampered validation of this finding in predominantly West-African replication sets. Our results suggest that established genetic risk factors play a role in African POAG, however, they do not explain the higher disease load. The high heterogeneity within Africans remains a challenge to identify the genetic commonalities for POAG in this ethnicity, and demands studies of extremely large size.

A multiethnic genome-wide association study of primary open-angle glaucoma identifies novel risk loci

Primary open-angle glaucoma (POAG) is a leading cause of irreversible vision loss, yet much of the genetic risk remains unaccounted for, especially in African-Americans who have a higher risk for developing POAG. We conduct a multiethnic genome-wide association study (GWAS) of POAG in the GERA cohort, with replication in the UK Biobank (UKB), and vice versa, GWAS in UKB with replication in GERA. We identify 24 loci (P < 5.0 × 10^-8), including 14 novel, of which 9 replicate (near FMNL2, PDE7B, TMTC2, IKZF2, CADM2, DGKG, ANKH, EXOC2, and LMX1B). Functional studies support intraocular pressure-related influences of FMNL2 and LMX1B, with certain Lmx1b mutations causing high IOP and glaucoma resembling POAG in mice. The newly identified loci increase the proportion of variance explained in each GERA race/ethnicity group, with the largest gain in African-Americans (0.5-3.1%). A meta-analysis combining GERA and UKB identifies 24 additional loci. Our study provides important insights into glaucoma pathogenesis.

Primary Open-Angle Glaucoma Genetics in African Americans

PURPOSE OF REVIEW

Individuals of African descent are at highest risk for developing primary open-angle glaucoma (POAG), a devastating disease and major contributor of blindness worldwide. Currently, there is a large dearth of knowledge in this area despite a critical need for better understanding the underlying genetic and environmental factors afflicting this population. Here we highlight the current literature exploring the genetics of POAG in African Americans.

RECENT FINDINGS

Current studies have yet to replicate European POAG index variants (i.e. CDKN2B-AS1 and SIX1/SIX6) in African Americans or to definitely exclude that these loci contribute to risk in African descent populations. Recent studies have evaluated clinical features that may account for some differences in POAG risk between African Americans and European Americans.

SUMMARY

In summary, little headway has been made in elucidating the genetics of primary open-angle glaucoma in African Americans and other individuals of African descent.

Major review: Molecular genetics of primary open-angle glaucoma

Glaucoma is a leading cause of irreversible blindness worldwide. Primary open-angle glaucoma (POAG), the most common type, is a complex inherited disorder that is characterized by progressive retinal ganglion cell death, optic nerve head excavation, and visual field loss. The discovery of a large, and growing, number of genetic and chromosomal loci has been shown to contribute to POAG risk, which carry implications for disease pathogenesis. Differential gene expression analyses in glaucoma-affected tissues as well as animal models of POAG are enhancing our mechanistic understanding in this common, blinding disorder. In this review we summarize recent developments in POAG genetics and molecular genetics research.