Inheritance of open-angle glaucoma in the Barbados family study

The Significance of Screening Family Members in Glaucoma: Opportunities and Challenges

PRECIS

This article delves into the imperative of screening family members of patients with glaucoma due to the disease's hereditary nature. It discusses the significant risks faced by first-degree relatives, approaches for identification, and challenges in implementing effective screening strategies. Emphasizing education, targeted campaigns, community involvement, and collaborative healthcare approaches, the article highlights the potential for mitigating undiagnosed glaucoma cases through strategic interventions targeting high-risk individuals.

PURPOSE

This article underscores the importance of screening family members of glaucoma patients, emphasizing the hereditary nature of the disease and the potential for screening to allow for early intervention to help prevent unnecessary vision loss.

METHODS/RESULTS

Glaucoma, affecting over 111.8 million by 2040, is relatively asymptomatic until late in the disease. Genetics predispose to glaucoma, with up to 70% heritability. High-risk individuals, particularly first-degree relatives, exhibit substantially elevated glaucoma risks-up to 22% compared with 2.3% in controls. Family history also correlates with greater disease severity. Identifying high-risk family members through cascade screenings for causative genes or direct examinations during proband visits emerges as efficient strategies. Challenges persist, including slow progression, healthcare accessibility, and ethical dilemmas in implementing family member screening. Challenges extend to the healthcare system, socioeconomic barriers, and familial communication issues. Efforts to educate probands and the public on the hereditary nature of glaucoma are pivotal. Tailored education campaigns, leveraging clinic visits, and community screenings, complemented by optometrist collaboration, form essential strategies.

CONCLUSIONS

Although challenges hinder family member screening, educating probands, targeted patient education, collaborative healthcare approaches, and community involvement offer promising avenues to combat undiagnosed glaucoma cases.

Evaluation of vessel density in healthy subjects with family history of glaucoma

OBJECTIVES

To investigate whether any microvascular changes are present in optic disc, peripapillary or maculary regions in healthy subjects with a family history of glaucoma.

METHODS

A total of 82 healthy subjects including 42 first-degree relatives of primary open-angle glaucoma (POAG) and 40 controls were enroled in this cross-sectional study. Global and sectoral vessel density (VD) measurements excluding large vessels, retina nerve fibre layer (RNFL) and macula ganglion cell (mGCC) thicknesses were obtained from a combined optical coherence tomography-angiography (OCT-A) and spectral-domain OCT system. Effect size (ES) was used for evaluating the magnitude of the statistically significant difference. Area under receiver operating characteristic curves (AUCs) were used to examine the ability of parameters to differentiate first-degree relatives to controls.

RESULTS

There was no significant difference in RNFL and mGCC thicknesses between groups. Although lower VD measurements in optic disc, peripapillary region, and macula were observed in the first-degree relatives, statistically significant mean difference (3.13 ± 0.87, p = 0.001) and large ES (0.80) were in only lower nasal sector of peripapillary region. Inter-eye asymmetry of supero-nasal VD was also statistically higher (3.74 ± 2.55 vs 1.89 ± 1.64) with a large ES in the first-degree relatives (p < 0.001, ES = 0.86). AUC for differentiating first-degree relatives from controls was highest for inter-eye asymmetry of supero-nasal sector VD (0.74, p < 0.001), followed by lower nasal sector VD (0.72, p < 0.001).

CONCLUSION

Compared to controls, first-degree relatives of patients with POAG were found to have significantly greater inter-eye asymmetry in supero-nasal peripapillary VD and less VD in the lower nasal peripapillary region.

Prospective study of glaucoma referrals across Europe: are we using resources wisely?

BACKGROUND

To investigate the outcomes of glaucoma referrals across different European countries.

METHODS

250 patients newly referred to tertiary referral glaucoma specialist practices in the UK, Hungary, Slovenia, Italy and Greece were prospectively enrolled (50 consecutive patients per centre). Referral accuracy and predictive value of referral criteria for an intervention or further monitoring (positive predictive value) were analysed.

RESULTS

Same-day discharges occurred in 43% (95% CI 39% to 75%) (12/28) of optometrist-initiated referrals (UK only), 37% (95% CI 30% to 45%) (59/158) of ophthalmologist-initiated referrals (all centres) and 54% (95% CI 40% to 68%) (26/48) of self-referrals (Hungary, Italy and Greece). The percentages from all referral sources were 46% (95% CI 32% to 60%) in the UK, 56% (95% CI 44% to 70%) in Hungary, 30% (95% CI 17% to 43%) in Slovenia, 22% (95% CI 11% to 34%) in Italy and 60% (95% CI 46% to 74%) in Greece (p<0.001). Overall, the referring criterion was confirmed in 54% (95% CI 45% to 63%) (64/119) for intraocular pressure (IOP) >21 mm Hg, 56% (95% CI 43% to 69%) (33/59) for a suspicious optic disc and 61% (95% CI 45% to 77%) (22/36) for a suspicious visual field, with large between-country differences (p<0.05 for all comparisons). Of all referrals, 32% (95% CI 26% to 37%) were initiated on the basis of IOP >21 mm Hg only. By combining the IOP criterion with any other referring criterion, the positive predictive value increased from 56% (95% CI 45% to 67%) to at least 89% (95% CI 68% to 100%). In the UK, a hypothetical IOP threshold of >26 mm Hg, as a requirement for IOP-only referrals, would reduce IOP-only referrals by 44%, while not missing any definite glaucoma cases.

CONCLUSION

The accuracy of referrals was poor in the UK and the other countries. Requiring a combination of criteria and raising the IOP threshold for IOP-only referrals are needed to cut waste in clinical care.

The inheritance of juvenile onset primary open angle glaucoma

Juvenile onset open angle glaucoma (JOAG) affects patients before 40 years of age, who present with high intraocular pressure and deep steep cupping of the optic nerve head. While it was considered to be inherited in an autosomal dominant fashion, recent studies have shown an autosomal recessive pattern as well as sporadic occurrence of the disease in several families. In this review, we analyze the genetic basis of the disease along with common mutations and their association with JOAG. We also analyzed the inheritance patterns in a large group of unrelated JOAG patients (n = 336) from Northern India wherein the prevalence of familial occurrence was assessed and segregation analysis performed, to determine the mode of inheritance.

Screening First Degree Relatives of Persons with Primary Open Angle Glaucoma in India

PURPOSE

To report the results of screening first degree relatives of persons identified with primary open angle glaucoma in a tertiary eye hospital glaucoma services.

DESIGN

A cross-sectional study of first degree relatives of persons with primary open angle glaucoma.

MATERIALS AND METHODS

First degree relatives of patients identified with primary open angle glaucoma were invited to participate in a screening evaluation in the base hospital to detect glaucoma. All participating individuals had comprehensive eye examination including vision screening, refraction, slit-lamp biomicroscopy, applanation tonometry, gonioscopy, frequency doubling peri-metry and dilated fundus examination. Persons with definite and suspected glaucoma were subject to full threshold automated perimetry.

RESULTS

A 514 first degree relatives of 346 persons with primary open angle glaucoma, of 4972 individuals who were invited to participate attended the screening examination (Response Rate 7%). Fifty-five percent of those who attended were males and mean age of participants was 56.8 years. Sixty-eight relatives (13.3% of those screened) were detected to have definite glaucoma. Sixty percent of those detected with definite glaucoma were siblings. Fifteen percent of siblings, 4% of off-springs and 20% of parents who attended the screening examination had definite open angle glaucoma.

CONCLUSION

Prevalence of open angle glaucoma amongst first degree relatives of persons with glaucoma is higher than in the general population as reported in previous studies. Significant barriers, however, exist in the uptake of eye care services among relatives of persons known to have primary open angle glaucoma. How to cite this article: Rajendrababu S, Gupta N, Vijayakumar B, Kumaragurupari R, Krishnadas SR. Screening First Degree Relatives of Persons with Primary Open Angle Glaucoma in India. J Curr Glaucoma Pract 2014;8(3):107-112.

CDKN2B polymorphism is associated with primary open-angle glaucoma (POAG) in the Afro-Caribbean population of Barbados, West Indies

The purpose of this study was to confirm previously reported associations of common variants in or near CDC7/TGFBR3, ZP4, SRBD1, ELOVL5, CAV1/CAV2, TLR4, CDKN2B, CDKN2B-AS1, ATOH7, PLXDC2, TMTC2, SIX1, and CARD10, with primary open angle glaucoma (POAG) in the Afro-Caribbean population of Barbados, West Indies. A total of 437 unrelated subjects from the Barbados Family Study of Open Angle Glaucoma (BFSG), including 272 with POAG and 165 unaffected individuals were included in this study. Eighteen SNPs were genotyped by using the multiplex SNaPshot method. Allelic, genotypic and model-based (dominant, recessive, and additive) associations of the SNPs with POAG were analyzed using Chi-squared tests and logistic regression. SNP rs1063192 (near CDKN2B) was found to be significantly associated with POAG (allelic P = 0.0008, genotypic P = 0.0029), and the minor allele C of rs1063192 was protective against POAG (OR  = 0.39; 95%CI  = 0.22−0.69). Suggestive association was also noted for rs7916697 (near ATHO7, allelic P  = 0.0096, genotypic P = 0.01) with the minor allele being protective (OR  = 0.67; 95% CI  = 0.50−0.91), although this finding did not withstand correction for multiple testing. However, a significant interactive effect on POAG risk was identified between rs1063192 and rs7916697 (P-interaction  = 2.80×10⁻⁵). Individuals with the rs1063192 protective genotype CC or CT and also rs7916697 genotypes GG or GA show a significantly decreased risk of POAG (OR = 0.17, 95%CI: 0.07−0.41). Our study confirms the significant association between SNP rs1063192 (CDKN2B, previously shown to influence vertical cup-to-disc ratio and POAG at 9p21) and POAG in the Afro-Caribbean population of Barbados. The minor allele of rs1063192 interacts with that of rs7916697 (ATOH7)) to reduce POAG risk. Our results also suggest that rs1063912 is a common protective variant for POAG in populations of African as well as European descent.

Risk factors for primary open-angle glaucoma in Japanese subjects attending community health screenings

Background/aims

To describe risk factors associated with primary open-angle glaucoma (POAG) in Japanese subjects who participated in community health screenings.

Methods

Residents of Akita, Japan, participating in a community health checkup were selected to undergo a comprehensive ophthalmic examination. Glaucoma was diagnosed based on optic disk appearance, perimetric results, and other ocular findings. Systemic blood pressure and intraocular pressure were measured and ocular perfusion pressure was calculated. Logistic regression analysis was performed to determine risk factors for POAG patients.

Results and conclusion

Of the 710 subjects examined, 26 had POAG. The estimated prevalence of POAG was 3.7%. After adjusting for age, the prevalence of POAG was similar to that found in the Tajimi Study of Japanese subjects. Multivariate logistic regression analysis demonstrated that older age (≥60 years, odds ratio [OR]: 3.49), lower diastolic blood pressure (≤58 mmHg, OR: 2.11), higher intraocular pressure (≥19 mmHg, OR: 4.12), and lower ocular perfusion pressure (≤34 mmHg, OR: 5.78) were associated with increased risk of having POAG. These findings may be relevant for identifying high risk groups.

Comparison of newly diagnosed ocular hypertension and open-angle glaucoma: ocular variables, risk factors, and disease severity

Purpose. To describe the distribution of ocular variables, risk factors, and disease severity in newly diagnosed ocular hypertension (OH) or open-angle glaucoma (OAG). Methods. Eligible subjects underwent a complete history and examination. Adjusted odds ratios (ORs) and 95% confidence intervals (CIs) obtained from multiple logistic regression models were used to compare OAG to OH and advanced to early/moderate OAG. Results. 405 subjects were enrolled: 292 (72.1%) with OAG and 113 (27.9%) with OH. 51.7% had early, 27.1% moderate, and 20.9% advanced OAG. The OR for OAG versus OH was 8.19 (P < 0.0001) for disc notch, 5.36 (P < 0.0001) for abnormal visual field, 1.45 (P = 0.001) for worsening mean deviation, 1.91 (P < 0.0001) for increased cupping, 1.03 for increased age (P = 0.030), and 0.36 (P = 0.010) for smoking. Conclusions. Increased age was a risk for OAG, and smoking decreased the risk of OAG compared to OH. Almost half of the OAG subjects had moderate/advanced disease at diagnosis.

Common variants on chromosome 2 and risk of primary open-angle glaucoma in the Afro-Caribbean population of Barbados

Primary open-angle glaucoma (POAG) is the second leading cause of blindness worldwide. Although a number of genetic loci have shown association or genetic linkage to monogenic forms of POAG, the identified genes and loci do not appear to have a major role in the common POAG phenotype. We seek to identify genetic loci that appear to be major risk factors for POAG in the Afro-Caribbean population of Barbados, West Indies. We performed linkage analyses in 146 multiplex families ascertained through the Barbados Family Study of Glaucoma (BFSG) and identified a strong linkage signal on chromosome 2p (logarithm of odds score = 6.64 at = 0 with marker D2S2156). We subsequently performed case-control analyses using unrelated affected individuals and unaffected controls. A set of SNPs on chromosome 2p was evaluated in two independent groups of BFSG participants, a discovery group (130 POAG cases, 65 controls) and a replication group (122 POAG cases, 65 controls), and a strong association was identified with POAG and rs12994401 in both groups (P < 3.34 E-09 and P < 1.21E-12, respectively). The associated SNPs form a common disease haplotype. In summary, we have identified a locus with a major impact on susceptibility to the common POAG phenotype in an Afro-Caribbean population in Barbados. Our approach illustrates the merit of using an isolated population enriched with common disease variants as an efficient method to identify genetic underpinning of POAG.

Susceptibility to glaucoma: differential comparison of the astrocyte transcriptome from glaucomatous African American and Caucasian American donors

Comparison of gene expression in normal and glaucomatous eyes from Caucasian American and African American donors reveals differences that might reflect different susceptibility to glaucoma.

Background

Epidemiological and genetic studies indicate that ethnic/genetic background plays an important role in susceptibility to primary open angle glaucoma (POAG). POAG is more prevalent among the African-descent population compared to the Caucasian population. Damage in POAG occurs at the level of the optic nerve head (ONH) and is mediated by astrocytes. Here we investigated differences in gene expression in primary cultures of ONH astrocytes obtained from age-matched normal and glaucomatous donors of Caucasian American (CA) and African American (AA) populations using oligonucleotide microarrays.

Results

Gene expression data were obtained from cultured astrocytes representing 12 normal CA and 12 normal AA eyes, 6 AA eyes with POAG and 8 CA eyes with POAG. Data were normalized and significant differential gene expression levels detected by using empirical Bayesian shrinkage moderated t-statistics. Gene Ontology analysis and networks of interacting proteins were constructed using the BioGRID database. Network maps included regulation of myosin, actin, and protein trafficking. Real-time RT-PCR, western blots, ELISA, and functional assays validated genes in the networks.

Conclusion

Cultured AA and CA glaucomatous astrocytes retain differential expression of genes that promote cell motility and migration, regulate cell adhesion, and are associated with structural tissue changes that collectively contribute to neural degeneration. Key upregulated genes include those encoding myosin light chain kinase (MYLK), transforming growth factor-β receptor 2 (TGFBR2), rho-family GTPase-2 (RAC2), and versican (VCAN). These genes along with other differentially expressed components of integrated networks may reflect functional susceptibility to chronic elevated intraocular pressure that is enhanced in the optic nerve head of African Americans.

Risk Factors for Incident Open-angle Glaucoma

PURPOSE

To evaluate risk factors for definite open-angle glaucoma (OAG), based on African-descent participants of the Barbados Eye Studies.

DESIGN

Cohort study with 81% to 85% participation over 9 years' follow-up.

PARTICIPANTS

We evaluated 3222 persons at risk, 40 to 84 years old, who did not have definite OAG at baseline.

METHODS

Participants had standardized study visits at baseline and after 4 and 9 years, with structured interviews, blood pressure (BP), and other measurements. The ophthalmic protocol included automated perimetry, applanation tonometry, fundus photography, and comprehensive ophthalmologic examinations for those referred. Central corneal thickness (CCT) was measured in a subset at the 9-year examination. Incidence was estimated by the product-limit approach; relative risk ratios (RRs) with 95% confidence intervals (CIs) were based on Cox regression models with discrete time.

MAIN OUTCOME MEASURE

Nine-year incidence of definite OAG.

RESULTS

Over 9 years, 125 persons developed definite OAG (incidence, 4.4%; 95% CI, 3.7-5.2). Baseline factors influencing risk were age (RR, 1.04; 95% CI, 1.02-1.05 per year); family history of glaucoma (RR, 2.4; 95% CI, 1.3-4.6); higher intraocular pressure (IOP) (RR, 1.12; 95% CI, 1.08-1.16 per mmHg); lower systolic BP (RR, 0.91; 95% CI, 0.84-1.00 per 10 mmHg); and lower ocular systolic, diastolic, and mean perfusion pressures (RR, 0.66; 95% CI, 0.54-0.80 per 10 mmHg higher mean perfusion pressure) (RR, 2.6; 95% CI, 1.4-4.6 for low mean perfusion pressure [<40 mmHg]). Thinner CCT was also associated with OAG incidence (odds ratio, 1.41; 95% CI, 1.01-1.96 per 40 mum lower).

CONCLUSIONS

This is the first report of risk factors for long-term OAG incidence; it is also based on a sizable number of new cases. Incidence was high in this African-descent population, where the established factors of older age, higher IOP, and family history contributed to risk. Additional predictors were vascular factors, including lower systolic BP, and particularly lower ocular perfusion pressures, which more than doubled risk. Thinner CCT was also a factor. These findings indicate a multifactorial etiology of OAG and suggest that similar risk factors apply across populations. Results are relevant for understanding OAG causation and identifying groups at high risk.

Targeting relatives of patients with primary open angle glaucoma: the help the family glaucoma project

PURPOSE

To assess the knowledge of patients with open angle glaucoma (OAG) and their family members about OAG risk factors and to study the referral of family members for eye examinations.

DESIGN

Cross-sectional survey and prospective cohort study.

METHODS

We interviewed OAG patients (probands) at the Wilmer Eye Institute and their biologically related parents, siblings, and children about their knowledge of OAG risk factors. Qualified family members were offered an eye examination through the EyeCare America program. Three months after initial contact, a follow-up telephone questionnaire determined the outcome of the referral.

RESULTS

Among 102 probands and 100 (of 230 eligible) family members who were interviewed, there was high awareness that OAG is related to older age (85% both groups). More probands knew of the association with higher intraocular pressure (95%) compared with family (78%). Yet, 21% of both groups were not aware that OAG is hereditary, and only 53% of probands and 30% of family members knew that OAG is more common in certain ethnic groups. Only two-thirds of probands had suggested that family members have an eye examination. Eighty percent of family members had had an eye examination within the last year; of 21 with no recent examination, 66% (13/21) accepted referral.

CONCLUSIONS

The Help the Family Glaucoma project developed a novel approach to identify those at high-risk for OAG. Screening of relatives of OAG patients deserves further study in a more representative selection of the general population.

Risk Factors and Open-angle Glaucoma: Classification and Application

Decades of epidemiologic research into open-angle glaucoma have elucidated several risk factors related in some way to the disease. As more and more risk factors are identified, however, assessing their individual and collective contributions in a particular patient is becoming increasingly complicated. To help organize our knowledge of risk in glaucoma we first review some concepts of risk and then propose a scheme that places known risk factors into categories (state of the individual, ocular anatomy and physiology, signs of disease, non-glaucoma medications, and personal behaviors) and also indicates how each factor interacts with disease (incidence, prevalence, progression, therapy.) We also describe methods for using risk factors in clinical practice and describe ways that a large and complex body of knowledge can be applied to individual patients.

Nine-Year Incidence of Open-Angle Glaucoma in the Barbados Eye Studies

PURPOSE

To determine the 9-year incidence of open-angle glaucoma (OAG) in African-descent participants of the Barbados Eye Studies.

DESIGN

Nine-year cohort study with 81% to 85% participation.

PARTICIPANTS

Three thousand two hundred twenty-two persons without definite OAG at baseline, at risk of developing OAG at follow-up.

METHODS

The standardized protocol included automated perimetry and various ophthalmic measurements, with a comprehensive ophthalmologic examination for those referred. Fundus photographs were evaluated independently by masked graders. Incidence was estimated by the product-limit approach. Relative risk (RR) ratios with 95% confidence intervals (CIs) were based on Cox regression models with discrete time.

MAIN OUTCOME MEASURE

Nine-year incidence of definite OAG, based on the development of visual field defects and glaucomatous optic neuropathy, with ophthalmologic confirmation.

RESULTS

The 9-year incidence of definite OAG was 4.4% (95% CI, 3.7%-5.2%), or an average of 0.5%/year, based on 125 new cases. Incidence increased greatly with age, from 2.2% at ages 40 to 49 years to 7.9% at ages 70 years or older, and tended to be higher in men than women (4.9% vs. 4.1%; RR, 1.3; 95% CI, 0.9-1.8). More than half (53%) of new cases were undetected, and of these, one third had intraocular pressure of 21 mmHg or less. When 141 persons developing suspected/probable OAG were considered, the total incidence was 9.4% (8.4%-10.6%), averaging approximately 1%/year, also increasing with age, and significantly higher in men than women (10.7% vs. 8.6%; RR, 1.31; 95% CI, 1.02-1.67).

CONCLUSIONS

These new data provide a measure of the long-term risk of OAG in an African-descent population, which is markedly higher than in persons of European ancestry. Results confirm the increased risk with age and in men. The incidence data fill a gap in our understanding of OAG risk and have implications for public health policy and planning; they also will allow the study of factors related to the risk of OAG development.

FGF19 is a target for FOXC1 regulation in ciliary body-derived cells

The forkhead C1 (FOXC1) transcription factor is involved in the development and regulation of several organs, including the eye, where FOXC1 alterations cause iris, trabecular meshwork and corneal anomalies. Using nickel agarose chromatin enrichment with human anterior segment cells, we previously identified the fibroblast growth factor 19 (FGF19) locus as a gene potentially regulated by FOXC1. Here, we demonstrate that FGF19 is a direct target of FOXC1 in the eye. FOXC1 positively regulates FGF19 expression in corneal and periocular mesenchymal cells in cell culture and in zebrafish embryos. Through the FGFR4 tyrosine kinase, FGF19 promotes MAPK phosphorylation in the developing and mature cornea. During development, loss of either FOXC1 or FGF19 results in complementary, but distinct, anterior segment dysgeneses. This study reveals an important role for FOXC1 in the direct regulation of the FGF19-FGFR4-MAPK pathway to promote both the development and maintenance of anterior segment structures within the eye.

Longitudinal glaucoma screening for siblings of patients with primary open angle glaucoma: the Nottingham Family Glaucoma Screening Study

AIMS

To assess the prevalence and cumulative incidence of open angle glaucoma (OAG) in a cohort group of siblings of OAG probands.

METHODS

Between 1994 and 2003, a group of siblings of OAG probands underwent both initial and follow up standardised ophthalmic examinations. Siblings were classified as "definite glaucoma" (primary OAG (POAG) and normal tension glaucoma (NTG)), "glaucoma suspects" (NTG suspects or ocular hypertension (OHT)), and normal. The prevalence and cumulative incidence of OAG over the follow up interval were calculated.

RESULTS

At the initial study, 271 siblings (mean age 63.6 years; female to male ratio 1.2) from 156 probands were examined. 32 (11.8%) were classified as definite glaucoma and 15 (5.5%) as suspects. In the follow up study, 157 of the 224 "normal" siblings from the initial study were examined (mean interval from initial study 7.0 (SD 1.0) years). 11 (7%) were classified as definite glaucoma and 30 (19.1%) as suspects. There were significant trends of increasing prevalence and incidence of OAG with age and a lifetime risk estimated at approximately 20% by age 70.

CONCLUSION

Siblings of glaucoma patients have an increased risk of developing glaucoma and the risk increases with age. An effective and repeated screening programme should be considered for this high risk group.

Commingling Analysis of Intraocular Pressure and Glaucoma in an Older Australian Population

PURPOSE

To test the hypothesis of a major genetic determinant of intraocular pressure (IOP) under the mixed genetic model in a defined population, and to elucidate the relationship between IOP and glaucoma.

METHODS

IOP was measured in 3654 persons attending the Blue Mountains Eye Study. A commingling analysis on IOP was performed using a new program, SKUDRIVER. The goodness of fit of 1-, 2- and 3-distribution models was measured. This was repeated after the glaucoma cases had been removed from the dataset, and further repeated on the glaucoma cases in the dataset.

RESULTS

The best model was 3-distribution with no evidence for Hardy-Weinberg disequilibrium. The proportion of variance explained by this major effect was 0.18. When glaucoma cases were removed, the best model had 2 distributions. There was no evidence of admixture in glaucoma patients.

CONCLUSIONS

The findings of this study are consistent with the presence of a major gene accounting for 18% of the variance of IOP, which could therefore influence the risk of glaucoma, in this population. These findings suggest methods of optimizing strategies for family and association studies to identify quantitative trait loci for IOP. No evidence for distinct IOP-dependent and IOP-independent subgroups of glaucoma was found.

A genome-wide scan for primary open-angle glaucoma (POAG): the Barbados Family Study of Open-Angle Glaucoma

Primary open-angle glaucoma (POAG) is characterized by damage to the optic nerve with associated loss of vision. Six named genetic loci have been identified as contributing to POAG susceptibility by genetic linkage analysis of mostly Caucasian families, and two of the six causative genes have been identified. The Barbados Family Study of Open-Angle Glaucoma (BFSG) was designed to evaluate the genetic component of POAG in a population of African descent. A genome-wide scan was performed on 1327 individuals from 146 families in Barbados, West Indies. Linkage results were based on models and parameter estimates derived from a segregation analysis of these families, and on model-free analyses. Two-point LOD scores >1.0 were identified on chromosomes 1, 2, 9, 10, 11, and 14, with increased multipoint LOD scores being found on chromosomes 2, 10, and 14. Fine mapping was subsequently carried out and indicated that POAG may be linked to intervals on chromosome 2q between D2S2188 and D2S2178 and chromosome 10p between D10S1477 and D10S601. Heterogeneity testing strongly supports linkage for glaucoma to at least one of these regions and suggests possible linkages to both. Although TIGR/myocilin and optineurin mutations have been shown to be causally linked to POAG in other populations, findings from this study do not support either of these as causative genes in an Afro-Caribbean population known to have relatively high rates of POAG.

Genetic basis of glaucoma

The application of molecular genetic techniques to the study of glaucoma has accelerated greatly during the past few years. In addition to localizing and identifying genes for specific types of glaucoma, researchers have begun to characterize the gene products and investigate molecular mechanisms involved in glaucoma. Much research has been focused on the gene expression, protein processing, and mutations of MYOC/TIGR, which is associated with both juvenile-and adult-onset primary open angle glaucoma. Investigations of other glaucoma-related genes, such as PITX2, FOXC1, and CYP1B1, are enabling a better understanding of anterior segment development and its relation to glaucoma.