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

Lack of association between SIX1/SIX6 locus polymorphisms and pseudoexfoliation syndrome in a population from the Republic of Korea

Previous studies have reported the association of the SIX1/SIX6 locus with open-angle glaucoma in various ethnic populations. However, the relevance of the SIX1/SIX6 locus to pseudoexfoliation syndrome (XFS) appears uncertain at present. Thus, we investigated the relationship between polymorphisms in the SIX1/SIX6 locus and XFS in a Korean XFS cohort. A total of 246 participants comprising 167 unrelated Korean patients with XFS and 79 ethnically matched control subjects were recruited. Four polymorphisms of the SIX1/SIX6 locus (rs33912345, rs12436579, rs2179970, and rs10483727) were genotyped using a TaqMan® allelic discrimination assay. Genotypic and allelic associations were analyzed using logistic regression. The minor allele frequency (MAF) of rs33912345 was found to be 0.287 and 0.247 in the XFS cases and controls, respectively, and the MAF of rs12436579 was found to be 0.383 and 0.361 in the XFS cases and control subjects, respectively. The MAF of rs2179970 was found to be 0.090 and 0.095 in the XFS cases and control subjects, respectively, and the MAF of rs10483727 was found to be 0.293 and 0.253 in the XFS cases and control subjects, respectively. Genetic association analysis of 4 SIX1/SIX6 locus single nucleotide polymorphisms (SNPs) revealed no significant difference in genotype distribution between the XFS cases and control subjects in the allelic, dominant, or recessive models (all, P > .05). The current study suggested that SIX1/SIX6 locus polymorphisms (rs33912345, rs12436579, rs2179970, and rs10483727) may not be associated with a genetic susceptibility to XFS in a Korean cohort.

The African Descent and Glaucoma Evaluation Study (ADAGES) III: Contribution of Genotype to Glaucoma Phenotype in African Americans: Study Design and Baseline Data

PURPOSE

To describe the study protocol and baseline characteristics of the African Descent and Glaucoma Evaluation Study (ADAGES) III.

DESIGN

Cross-sectional, case-control study.

PARTICIPANTS

Three thousand two hundred sixty-six glaucoma patients and control participants without glaucoma of African or European descent were recruited from 5 study centers in different regions of the United States.

METHODS

Individuals of African descent (AD) and European descent (ED) with primary open-angle glaucoma (POAG) and control participants completed a detailed demographic and medical history interview. Standardized height, weight, and blood pressure measurements were obtained. Saliva and blood samples to provide serum, plasma, DNA, and RNA were collected for standardized processing. Visual fields, stereoscopic disc photographs, and details of the ophthalmic examination were obtained and transferred to the University of California, San Diego, Data Coordinating Center for standardized processing and quality review.

MAIN OUTCOME MEASURES

Participant gender, age, race, body mass index, blood pressure, history of smoking and alcohol use in POAG patients and control participants were described. Ophthalmic measures included intraocular pressure, visual field mean deviation, central corneal thickness, glaucoma medication use, or past glaucoma surgery. Ocular conditions, including diabetic retinopathy, age-related macular degeneration, and past cataract surgery, were recorded.

RESULTS

The 3266 ADAGES III study participants in this report include 2146 AD POAG patients, 695 ED POAG patients, 198 AD control participants, and 227 ED control participants. The AD POAG patients and control participants were significantly younger (both, 67.4 years) than ED POAG patients and control participants (73.4 and 70.2 years, respectively). After adjusting for age, AD POAG patients had different phenotypic characteristics compared with ED POAG patients, including higher intraocular pressure, worse visual acuity and visual field mean deviation, and thinner corneas (all P < 0.001). Family history of glaucoma did not differ between AD and ED POAG patients.

CONCLUSIONS

With its large sample size, extensive specimen collection, and deep phenotyping of AD and ED glaucoma patients and control participants from different regions in the United States, the ADAGES III genomics study will address gaps in our knowledge of the genetics of POAG in this high-risk population.

Family-based analysis identified CD2 as a susceptibility gene for primary open angle glaucoma in Chinese Han population

Primary open angle glaucoma (POAG) is characterized by optic disc cupping and irreversible loss of retinal ganglion cells. Few genes have been detected that influence POAG susceptibility and little is known about its genetic architecture. In this study, we employed exome sequencing on three members from a high frequency POAG family to identify the risk factors of POAG in Chinese population. Text-mining method was applied to identify genes associated with glaucoma in literature, and protein-protein interaction networks were constructed. Furthermore, reverse transcription PCR and Western blot were performed to confirm the differential gene expression. Six genes, baculoviral inhibitors of apoptosis protein repeat containing 6 (BIRC6), CD2, luteinizing hormone/choriogonadotropin receptor (LHCGR), polycystic kidney and hepatic disease gene 1 (PKHD1), phenylalanine hydroxylase (PAH) and fucosyltransferase 7 (FUT7), which might be associated with POAG, were identified. Both the mRNA expression levels and protein expression levels of HSP27 were increased in astrocytes from POAG patients compared with those from normal control, suggesting that mutation in CD2 might pose a risk for POAG in Chinese population. In conclusion, novel rare variants detected by exome sequencing may hold the key to unravelling the remaining contribution of genetics to complex diseases such as POAG.

Progress toward personalized medicine for glaucoma

How will you respond when a patient asks, "Doctor, what can I do to prevent myself from going blind from glaucoma like mom?". There is optimism that genetic profiling will help target patients to individualized treatments based on validated disease risk alleles, validated pharmacogenetic markers and behavioral modification. Personalized medicine will become a reality through identification of disease and pharmacogenetic markers, followed by careful study of how to employ this information in order to improve treatment outcomes. With advances in genomic technologies, research has shifted from the simple monogenic disease model to a complex multigenic and environmental disease model to answer these questions. Our challenges lie in developing risk models that incorporate gene-gene interactions, gene copy-number variations, environmental interactions, treatment effects and clinical covariates.

Expansive marker analysis replicating the association of glaucoma susceptibility with human chromosome loci 1q43 and 10p12.31

Three human chromosome loci (1q43, 10p12.31, and 12q21.31) were recently associated with the susceptibility to primary open-angle glaucoma (POAG) in a Japanese population; however, this was not replicated in three subsequent studies using South Indian, Afro-Caribbean, and Chinese populations. To identify genetic markers that are robustly associated across ethnic populations, numerous markers in addition to the six in the three reported loci were examined in this study. A total of 31 single-nucleotide polymorphism (SNP) markers were genotyped for 1115 Korean participants, and many neighboring SNPs were imputed using the Korean HapMap Project genotype data. Each SNP was statistically tested for association with POAG susceptibility by comparisons among 211 POAG patients with 904 unaffected controls. A strong and statistically significant association was found with a previously unreported SNP, rs7098387 (odds ratio, OR=2.0 (1.4-3.0), P=0.00038) at the 10p12.31 locus (where 11 SNPs were typed and 38 imputed) in contrast to the reported rs7081455, which was too poorly correlated with newly associated rs7098387 (r2=0.003, D'=0.40) to show association. Additionally, a modest association was observed with the reported rs693421 (OR=1.4 (1.1-1.7), P=0.0082) and several other SNPs located within and around ZP4 at the 1q43 locus (10 SNPs typed and 14 imputed). However, no association was observed with the reported rs7961953 SNP or any other SNPs at the 12q21.31 locus, upstream of TMTC2 (10 SNPs typed and 29 imputed). Accordingly, POAG susceptibility association was replicated using rs7098387 (C) rather than rs7081455 (T) at the 10p12.31 locus and additionally with rs693421 (T) at the 1q43 locus.

The genetics of pigment dispersion syndrome and pigmentary glaucoma

We review the inheritance patterns and recent genetic advances in the study of pigment dispersion syndrome (PDS) and pigmentary glaucoma (PG). Both conditions may result from combinations of mutations in more than one gene or from common variants in many genes, each contributing small effects. We discuss the currently known genetic loci that may be related with PDS/PG in humans, the role of animal models in expanding our understanding of the genetic basis of PDS, the genetic factors underlying the risk for conversion from PDS to PG and the relationship between genetic and environmental--as well as anatomical--risk factors.

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.

Genetics of primary glaucoma

PURPOSE OF REVIEW

To provide an overview of the genetics of the primary open-angle glaucomas with particular attention to congenital, infantile, and juvenile forms.

RECENT FINDINGS

Mutations in CYP1B1, in addition to being the most common identifiable cause of autosomal recessive primary congenital/infantile glaucoma, can infrequently underlie juvenile and even primary adult-onset open-angle glaucoma, particularly in certain consanguineous populations. In 2009, patients diagnosed with congenital/infantile glaucoma were found to have recessive mutations in a second gene, LTBP2, with a phenotypic spectrum that includes primary megalocornea, spherophakia with ectopia lentis, and lens-related glaucoma. The most common identifiable cause of primary juvenile open-angle glaucoma across most populations remains heterozygous (autosomal dominant) MYOC mutation, underlying up to one-third of cases and possibly sometimes involved in earlier and later onset glaucomas Although primary adult-onset open-angle glaucoma usually does not follow simple Mendelian genetics and is etiologically complex, genome-wide association studies are uncovering genetic susceptibility factors. In some cases, primary adult-onset open-angle glaucoma can be caused by heterozygous mutation in MYOC, OPTN, or WDR36. In addition, in 2009, heterozygous NTF4 mutation was associated with the phenotype in a small percentage of patients from a German cohort.

SUMMARY

Seemingly unaffected siblings of children with CYP1B1-related primary congenital/infantile glaucoma should undergo genetic testing because of variable expressivity for the phenotype; such testing should also be considered for other asymptomatic relatives, especially in consanguineous families. In western populations, dominant MYOC mutation remains a common cause of primary open-angle juvenile glaucoma and infrequently can be implicated in congenital/infantile or adult-onset forms; identified families should undergo genetic counseling. Primary adult-onset open-angle glaucoma rarely follows simple Mendelian genetics, but genomic studies in different populations are revealing potential genetic risk factors for the phenotype.

Current concepts on primary open-angle glaucoma genetics: a contribution to disease pathophysiology and future treatment

Glaucoma is a common, complex, heterogenous disease and it constitutes the major cause of irreversible blindness worldwide. Primary open-angle glaucoma (POAG) is the most common type of glaucoma in all populations. Most of the molecular mechanisms leading to POAG development are still unknown. Gene mutations in various populations have been identified by genetic studies and a genetic basis for glaucoma pathogenesis has been established. Linkage analysis and association studies are genetic approaches in the investigation of the genetic basis of POAG. Genome-wide association studies (GWAS) are more powerful compared with linkage analysis in discovering genes of small effect that might contribute to the development of the disease. POAG links to at least 20 genetic loci, but only 2 genes identified in these loci, myocilin and optineurin, are considered as well-established glaucoma-causing genes, whereas the role of other loci, genes, and variants implicated in the development of POAG remains controversial. Gene mutations associated with POAG result in retinal ganglion cell death, which is the common outcome of pathogenetic mechanisms in glaucoma. In future, if the sensitivity and specificity of genotyping increases, it may be possible to screen individuals routinely for disease susceptibility. This review is an update on the latest progress of genetic studies associated with POAG. It emphasizes the correlation of recent achievements in genetics with glaucoma pathophysiology, glaucoma treatment perspectives, and the possibility of future prevention of irreversible visual loss caused by the disease.

Screening for OPTN mutations in amyotrophic lateral sclerosis in a mainly Caucasian population

Mutations in the optineurin (OPTN) gene cause amyotrophic lateral sclerosis (ALS). We previously reported 3 types of OPTN mutation in Japanese ALS subjects. Here, to identify the OPTN mutations in individuals of different ethnicity, we screened 563 sporadic ALS (SALS) subjects and 124 familial ALS (FALS) subjects who were mainly Caucasian. We found a c.964T>C synonymous variation in exon 8. However, we could not find the meaningful OPTN mutations. The results indicate that OPTN mutations causing ALS are rare, especially in mainly Caucasian ALS subjects.

Complex genetic mechanisms in glaucoma: an overview

Glaucomas comprise a group of hereditary optic neuropathies characterized by progressive and irreversible visual field loss and damage to the optic nerve head. It is a complex disease with multiple molecular mechanisms underlying its pathogenesis. Genetic heterogeneity is the hallmark of all glaucomas and multiple chromosomal loci have been linked to the disease, but only a few genes have been characterized, viz. myocilin (MYOC), optineurin (OPTN), WDR36 and neurotrophin-4 (NTF4) in primary open angle glaucoma (POAG) and CYP1B1 and LTBP2 in congenital and developmental glaucomas. Case-control-based association studies on candidate genes involved in different stages of glaucoma pathophysiology have indicated a very limited involvement. The complex mechanisms leading to glaucoma pathogenesis indicate that it could be attributed to multiple genes with varying magnitudes of effect. In this review, we provide an appraisal of the various efforts in unraveling the molecular mystery in glaucoma and also some future directions based on the available scientific knowledge and technological developments.

Evidence for RPGRIP1 gene as risk factor for primary open angle glaucoma

Glaucoma is a genetically heterogeneous disorder and is the second cause of blindness worldwide owing to the progressive degeneration of retinal ganglion neurons. Very few genes causing glaucoma were identified to this date. In this study, we screened 10 candidate genes of glaucoma between the D14S261 and D14S121 markers of chromosome 14q11, a critical region previously linked to primary open-angle glaucoma (POAG). Mutation analyses of two large cohorts of patients with POAG, normal tension glaucoma (NTG) and juvenile open-angle glaucoma (JOAG), and control subjects, found only association of non-synonymous heterozygous variants of the retinitis pigmentosa GTPase regulator-interacting protein 1 (RPGRIP1) with POAG, NTG and JOAG. The 20 non-synonymous variants identified in RPGRIP1 were all distinct from variants causing photoreceptor dystrophies and were found throughout all but one domain (RPGR-interacting domain) of RPGRIP1. Among them, 14 missense variants clustered within or around the C2 domains of RPGRIP1. Yeast two-hybrid analyses of a subset of the missense mutations within the C2 domains of RPGRIP1 shows that five of them (p.R598Q, p.A635G, p.T806I, p.A837G and p.I838V) decrease the association of the C2 domains with nephrocystin-4 (NPHPH). When considering only these five confirmed C2-domain mutations, the association remains statistically significant (P=0.001). Altogether, the data support that heterozygous non-synonymous variants of RPGRIP1 may cause or increase the susceptibility to various forms of glaucoma and that among other factors, physical impairment of the interaction of RPGRIP1with different proteins may contribute to the pathogenesis of forms of glaucoma.

Glaucoma: genes, phenotypes, and new directions for therapy

Glaucoma, a leading cause of blindness worldwide, is characterized by progressive optic nerve damage, usually associated with intraocular pressure. Although the clinical progression of the disease is well defined, the molecular events responsible for glaucoma are currently poorly understood and current therapeutic strategies are not curative. This review summarizes the human genetics and genomic approaches that have shed light on the complex inheritance of glaucoma genes and the potential for gene-based and cellular therapies that this research makes possible.

Hyperdiagnostics: postcolonial utopics of race-based biomedicine

The expansion of biomedical research into countries outside the United States and Western Europe is positing new biological links between populations based on race. This expansion includes six international projects occurring in Barbados, premised on the idea that the population is genetically representative of other black people. Based on ethnographic research tracking one such study, a genetics of asthma project, this article explores the ways Caribbean meanings of ethnicity and illness are reworked as Barbadian state medical practitioners become involved in facilitating the international genetics research on race and disease. As the state attempts to participate in an imagined future of genetic medicine, the hyperspecificity of genetic technologies create new medical meanings of race and disease. These changes rely on a paradoxical response by medical practitioners toward the high technology American genetic research as both authoritative and inapplicable, creating unexpected etiologies of illness and ethnicity.

Development of novel drugs for ocular diseases: possibilities for individualized therapy

In clinical ophthalmology, new and old drug regimens are available for the treatment of major eye diseases, including potentially blinding conditions, such as glaucoma, and various macular diseases. In glaucoma, therapeutic treatment mainly deals with control of intraocular pressure at low levels but the clinical courses of patients can be very variable. Very often, specific drug combinations and dosages have to be formulated for individual glaucoma patients. In neovascular age-related macular degeneration, choroidal neovascularization can lead to progressive and irreversible visual impairment if not treated early. In recent years, clinical trials using photodynamic therapy with verteporfin and various anti-VEGF antibodies, such as ranibizumab and bevacizumab, have enhanced the treatment outcomes of neovascular age-related macular degeneration. In diabetic macular edema, intravitreal triamcinolone acetonide and anti-VEGF therapy are effective in some patients. Again, responses to treatment are not uniform in all macular patients. Traditional herbal medicine has long been known to play a role in the practice of personalized formulations in Asia. Potential preventive and therapeutic effects have been claimed in individual eye patients. Meanwhile, advanced technologies in molecular biology have led to identification of genes associated with many eye diseases and development of the concept of individual medicine, in which the genotype of a person can be used as a basis for disease prediction or prophylactic treatments. Moreover, pharmacogenomic studies have demonstrated the association of various genotypes or haplotypes with responses to drug therapies, providing hope for tailormade personalized treatments. The combination of genotypic information with clinical features for the prescription of treatment modes in eye diseases is under vigorous research.

Molecular complexity of primary open angle glaucoma: current concepts

Glaucoma is a group of heterogeneous optic neuropathies with complex genetic basis. Among the three principle subtypes of glaucoma, primary open angle glaucoma (POAG) occurs most frequently. Till date, 25 loci have been found to be linked to POAG. However, only three underlying genes (Myocilin, Optineurin and WDR36) have been identified. In addition, at least 30 other genes have been reported to be associated with POAG. Despite strong genetic influence in POAG pathogenesis, only a small part of the disease can be explained in terms of genetic aberration. Current concepts of glaucoma pathogenesis suggest it to be a neurodegenerative disorder which is triggered by different factors including mechanical stress due to intra-ocular pressure, reduced blood flow to retina, reperfusion injury, oxidative stress, glutamate excitotoxicity, and aberrant immune response. Here we present a mechanistic overview of potential pathways and crosstalk between them operating in POAG pathogenesis.

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.

Chromosomal Abnormalities and Glaucoma: A Case of Congenital Glaucoma with Trisomy 8q22-Qter/ Monosomy 9p23-Pter

PURPOSE

To present a case of congenital glaucoma with an unbalanced translocation trisomy 8q22-qter/monosomy 9p23-pter, resulting in trisomy of the GLC1D locus. To perform a literature review of chromosomal abnormalities associated with glaucoma.

METHOD

A case report of a family with balanced translocation without glaucoma and unbalanced translocation with congenital glaucoma. PubMed and OMIM databases were searched for reports of chromosomal abnormalities and glaucoma.

RESULTS

Other case reports of congenital glaucoma with chromosomal abnormalities in this region were identified. A review of cytogenetics in southeastern Australia found nine cases involving the loss of 9p23 and 10 cases involving mosaicism for trisomy 8, but none had congenital glaucoma. A review of the literature identified reports of glaucoma and chromosomal abnormalities in regions with glaucoma loci mapped by conventional linkage analysis. These include the loci GLC1B, GLC1C, GLC1D, GLC1F, GPDS1, and RIEG2.

CONCLUSION

The study of patients with glaucoma and chromosomal abnormalities may help to identify new glaucoma genes. Ophthalmologists can assist with this by requesting cytogenetic studies on congenital and developmental glaucoma cases and interacting with ophthalmic genetics researchers.

Null mutations in LTBP2 cause primary congenital glaucoma

Primary congenital glaucoma (PCG) is an autosomal-recessive condition characterized by high intraocular pressure (IOP), usually within the first year of life, which potentially could lead to optic nerve damage, globe enlargement, and permanent loss of vision. To date, PCG has been linked to three loci: 2p21 (GLC3A), for which the responsible gene is CYP1B1, and 1p36 (GLC3B) and 14q24 (GLC3C), for which the genes remain to be identified. Here we report that null mutations in LTBP2 cause PCG in four consanguineous families from Pakistan and in patients of Gypsy ethnicity. LTBP2 maps to chromosome 14q24.3 but is around 1.3 Mb proximal to the documented GLC3C locus. Therefore, it remains to be determined whether LTBP2 is the GLC3C gene or whether a second adjacent gene is also implicated in PCG. LTBP2 is the largest member of the latent transforming growth factor (TGF)-beta binding protein family, which are extracellular matrix proteins with multidomain structure. It has homology to fibrillins and may have roles in cell adhesion and as a structural component of microfibrils. We confirmed localization of LTBP2 in the anterior segment of the eye, at the ciliary body, and particularly the ciliary process. These findings reveal that LTBP2 is essential for normal development of the anterior chamber of the eye, where it may have a structural role in maintaining ciliary muscle tone.

Primary open angle glaucoma in subjects harbouring the predicted GLC1L haplotype reveals a normotensive phenotype

PURPOSE

Primary open angle glaucoma (POAG) is a complex heterogeneous disease. The aim of this study was to describe the POAG phenotype in individuals who harbour the novel GLC1L disease-associated haplotype in a large pedigree where the Myocilin Gln368STOP mutation also segregates.

METHODS

The clinical findings from 24 subjects with POAG from the GTAS02 family recruited as part of the Glaucoma Inheritance Study of Tasmania (GIST) were compared relative to genotype status. The previously identified GLC1L disease haplotype encompasses a chromosomal region of 8.3 centimorgans bounded by the markers D3S3521 and D3S1289 on 3p21-22.

RESULTS

In subjects with the GLC1L disease haplotype (with or without Gln368STOP), the POAG phenotype was characterized by a mean age at diagnosis of 54.3 years, and mean maximum recorded intraocular pressure (IOP) of 23.9 mmHg. The mean maximum recorded IOP was lower in subjects with the predicted disease haplotype and no Gln368STOP mutation, compared with subjects with the predicted disease haplotype and presence of the Gln368STOP mutation (P = 0.02). Presence of the Gln368STOP mutation was significantly more common in those with the predicted disease haplotype than those without (P = 0.04). In the four subjects carrying the GLC1L disease-associated haplotype without the Gln368STOP mutation, a normotensive glaucoma (mean maximum recorded IOP 15 mmHg, range 13-17 mmHg) was present.

CONCLUSIONS

The GLC1L locus may be associated with glaucoma in the absence of elevated IOP. Discovery of the specific gene within the GLC1L locus on 3p21-22 would provide a useful addition to our ability to offer genetic testing and counselling to POAG individuals and their families.

Gene expression and functional studies of the optic nerve head astrocyte transcriptome from normal African Americans and Caucasian Americans donors

PURPOSE

To determine whether optic nerve head (ONH) astrocytes, a key cellular component of glaucomatous neuropathy, exhibit differential gene expression in primary cultures of astrocytes from normal African American (AA) donors compared to astrocytes from normal Caucasian American (CA) donors.

METHODS

We used oligonucleotide Affymetrix microarray (HG U133A & HG U133A 2.0 chips) to compare gene expression levels in cultured ONH astrocytes from twelve CA and twelve AA normal age matched donor eyes. Chips were normalized with Robust Microarray Analysis (RMA) in R using Bioconductor. Significant differential gene expression levels were detected using mixed effects modeling and Statistical Analysis of Microarray (SAM). Functional analysis and Gene Ontology were used to classify differentially expressed genes. Differential gene expression was validated by quantitative real time RT-PCR. Protein levels were detected by Western blots and ELISA. Cell adhesion and migration assays tested physiological responses. Glutathione (GSH) assay detected levels of intracellular GSH.

RESULTS

Multiple analyses selected 87 genes differentially expressed between normal AA and CA (P<0.01). The most relevant genes expressed in AA were categorized by function, including: signal transduction, response to stress, ECM genes, migration and cell adhesion.

CONCLUSIONS

These data show that normal astrocytes from AA and CA normal donors display distinct expression profiles that impact astrocyte functions in the ONH. Our data suggests that differences in gene expression in ONH astrocytes may be specific to the development and/or progression of glaucoma in AA.

Density of common complex ocular traits in the aging eye: analysis of secondary traits in genome-wide association studies

Genetic association studies are identifying genetic risks for common complex ocular traits such as age-related macular degeneration (AMD). The subjects used for discovery of these loci have been largely from clinic-based, case-control studies. Typically, only the primary phenotype (e.g., AMD) being studied is systematically documented and other complex traits (e.g., affecting the eye) are largely ignored. The purpose of this study was to characterize these other or secondary complex ocular traits present in the cases and controls of clinic-based studies being used for genetic study of AMD. The records of 100 consecutive new patients (of any diagnosis) age 60 or older for which all traits affecting the eye had been recorded systematically were reviewed. The average patient had 3.5 distinct diagnoses. A subset of 10 complex traits was selected for further study because they were common and could be reliably diagnosed. The density of these 10 complex ocular traits increased by 0.017 log-traits/year (P = 0.03), ranging from a predicted 2.74 at age 60 to 4.45 at age 90. Trait-trait association was observed only between AMD and primary vitreomacular traction (P = 0.0009). Only 1% of subjects age 60 or older had no common complex traits affecting the eye. Extrapolations suggested that a study of 2000 similar subjects would have sufficient power to detect genetic association with an odds ratio of 2.0 or less for 4 of these 10 traits. In conclusion, the high prevalence of complex traits affecting the aging eye and the inherent biases in referral patterns leads to the potential for confounding by undocumented secondary traits within case-control studies. In addition to the primary trait, other common ocular phenotypes should be systematically documented in genetic association studies so that adjustments for potential trait-trait associations and other bias can be made and genetic risk variants identified in secondary analyses.

Recurrent Myocilin Asn480Lys glaucoma causative mutation arises de novo in a family of Andean descent

PURPOSE

To search for MYOC mutations in Peruvian primary open angle glaucoma (POAG) families.

PATIENTS AND METHODS

Two patients from each of the 11 POAG Peruvian families were screened for sequence variants in MYOC coding exons by conformational sensitive gel electrophoresis and sequencing was performed on the samples indicating probable sequence changes.

RESULTS

We detected 2 families bearing distortions of conformational sensitive gel electrophoresis indicating mutations. Sequencing of these samples revealed coding sequence changes. A native Andean descent family presented with a MYOC mutation, Asn480Lys (C-->G at nucleotide 1440). This is different from the previously reported C-->A change at nucleotide 1440 that causes Asn480Lys in 2 unrelated French and Dutch families with glaucoma of variable expressivity, and indicates a third independent event. A second family of admixed origin showed the presence of the known Arg76Lys polymorphism.

CONCLUSIONS

In the study of MYOC variants in 11 POAG Peruvian families, we have found a family of ethnically admixed origin with polymorphism Arg76Lys and a family of Andean descent bearing a third event of the Asn480Lys, the MYOC mutation that has been reported in the highest number of POAG patients (>80 cases). Analysis of this family could contribute with information about disease manifestation, progression, and treatment response in the context of a distinct genetic background and also climatic, altitude, and socioeconomical conditions.

DNA sequence variants in the LOXL1 gene are associated with pseudoexfoliation glaucoma in a U.S. clinic-based population with broad ethnic diversity

Background

Pseudoexfoliation syndrome is a major risk factor for glaucoma in many populations throughout the world. Using a U.S. clinic-based case control sample with broad ethnic diversity, we show that three common SNPs in LOXL1 previously associated with pseudoexfoliation in Nordic populations are significantly associated with pseudoexfoliation syndrome and pseudoexfoliation glaucoma.

Methods

Three LOXL1 SNPs were genotyped in a patient sample (206 pseudoexfoliation, 331 primary open angle glaucoma, and 88 controls) from the Glaucoma Consultation Service at the Massachusetts Eye and Ear Infirmary. The SNPs were evaluation for association with pseudeoexfoliation syndrome, pseudoexfoliation glaucoma, and primary open angle glaucoma.

Results

The strongest association was found for the G allele of marker rs3825942 (G153D) with a frequency of 99% in pseudoexfoliation patients (with and without glaucoma) compared with 79% in controls (p = 1.6 × 10^-15; OR = 20.93, 95%CI: 8.06, 54.39). The homozygous GG genotype is also associated with pseudoexfoliation when compared to controls (p = 1.2 × 10^-12; OR = 23.57, 95%CI: 7.95, 69.85). None of the SNPs were significantly associated with primary open angle glaucoma.

Conclusion

The pseudoexfoliation syndrome is a common cause of glaucoma. These results indicate that the G153D LOXL1 variant is significantly associated with an increased risk of pseudoexfoliation and pseudoexfoliation glaucoma in an ethnically diverse patient population from the Northeastern United States. Given the high prevalence of pseudooexfoliation in this geographic region, these results also indicate that the G153D LOXL1 variant is a significant risk factor for adult-onset glaucoma in this clinic based population.

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.

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.

Identification of novel genetic loci for intraocular pressure: a genomewide scan of the Beaver Dam Eye Study

OBJECTIVE

To identify genetic loci that control intraocular pressure (IOP).

METHODS

We performed a genomewide scan of IOP, using 486 pedigrees ascertained through a population-based cohort, the Beaver Dam Eye Study. Linkage analysis was performed using the modified Haseman-Elston regression models and variance components linkage analysis.

RESULTS

Seven regions of interest were identified on chromosomes 2, 5, 6, 7, 12, 15, and 19. The novel linkage region on chromosome 19p had an empirical multipoint P value of 6.1 x 10(-5). Two of the regions (2 and 19) were especially interesting since each has been identified as a potential linkage region for blood pressure.

CONCLUSIONS

The results of this genomewide scan provide evidence that a quantitative trait locus may influence elevated IOP and may colocalize with blood pressure loci. These loci may control systemic pressure reflected in the eye and vascular system.

CLINICAL RELEVANCE

Glaucoma is a leading cause of blindness in the world, and the identification of genes that contribute to this disease is essential. Elevated IOP is a principal risk factor for primary open-angle glaucoma and an intriguing quantitative trait that may strongly influence the development of disease.

Defining the human macula transcriptome and candidate retinal disease genes using EyeSAGE

PURPOSE

To develop large-scale, high-throughput annotation of the human macula transcriptome and to identify and prioritize candidate genes for inherited retinal dystrophies, based on ocular-expression profiles using serial analysis of gene expression (SAGE).

METHODS

Two human retina and two retinal pigment epithelium (RPE)/choroid SAGE libraries made from matched macula or midperipheral retina and adjacent RPE/choroid of morphologically normal 28- to 66-year-old donors and a human central retina longSAGE library made from 41- to 66-year-old donors were generated. Their transcription profiles were entered into a relational database, EyeSAGE, including microarray expression profiles of retina and publicly available normal human tissue SAGE libraries. EyeSAGE was used to identify retina- and RPE-specific and -associated genes, and candidate genes for retina and RPE disease loci. Differential and/or cell-type specific expression was validated by quantitative and single-cell RT-PCR.

RESULTS

Cone photoreceptor-associated gene expression was elevated in the macula transcription profiles. Analysis of the longSAGE retina tags enhanced tag-to-gene mapping and revealed alternatively spliced genes. Analysis of candidate gene expression tables for the identified Bardet-Biedl syndrome disease gene (BBS5) in the BBS5 disease region table yielded BBS5 as the top candidate. Compelling candidates for inherited retina diseases were identified.

CONCLUSIONS

The EyeSAGE database, combining three different gene-profiling platforms including the authors' multidonor-derived retina/RPE SAGE libraries and existing single-donor retina/RPE libraries, is a powerful resource for definition of the retina and RPE transcriptomes. It can be used to identify retina-specific genes, including alternatively spliced transcripts and to prioritize candidate genes within mapped retinal disease regions.

Complex genetics of complex traits: the case of primary open-angle glaucoma

Glaucoma, which is a complex heterogeneous disease, presents an ideal case for genetic investigation. Primary open-angle glaucoma (POAG) is the commonest subtype and will be the focus of this review. When detected early, POAG is amenable to therapeutic intervention. Unfortunately, current population-based clinical screening lacks efficacy. If individuals with a genetic predisposition for developing POAG can be identified, then efficient and cost-effective population-based screening programs could be designed. Although considerable inroads have been made in understanding the natural history of POAG caused by mutations in the myocilin and optineurin genes, other POAG genes accounting for most cases remain to be identified. This review explores the genetic mechanisms that have been unequivocally linked to the glaucomatous process and then discusses potential avenues for future breakthroughs.

Association of Apolipoprotein E Polymorphisms With Normal Tension Glaucoma in a Chinese Population

PURPOSE

To evaluate the role of apolipoprotein E (APOE) polymorphisms in primary open angle glaucoma (POAG).

METHODS

A cohort of 400 unrelated Chinese POAG patients was examined, including 294 cases of high tension glaucoma (HTG) and 106 with normal tension glaucoma (NTG). Also studied were 300 unrelated Chinese control subjects. The genotypes of the APOE polymorphisms in exon 4 and in the promoter at positions -491, -427, and -219 were determined by polymerase chain reaction and restriction endonuclease analysis. Frequencies of the genotypes were compared between patients and controls by chi test or Fisher exact test. The association of APOE polymorphisms with POAG phenotypes including age at diagnosis, intraocular pressure (IOP) at diagnosis, highest IOP, cup-disc ratio, and visual field score was investigated by the Kruskal-Wallis test.

RESULTS

No significant difference was detected in the frequencies of APOE promoter polymorphisms between POAG patients and control subjects (P>0.0125). For the exon 4 polymorphism, when compared with control subjects, the frequency of epsilon 4 carriers was significantly lower in patients with NTG (P=0.008; odds ratio=0.36, 95% confidence interval=0.17, 0.79) but not in HTG (P=0.07). Compared with -219TT, the -219G carriers had a significant higher age at diagnosis (P=0.0046). No significant association was found between other APOE polymorphisms and POAG phenotypes (P>0.07).

CONCLUSIONS

Our findings suggest that the APOE epsilon 4 allele confers a protective effect against NTG, whereas the APOE promoter polymorphisms do not contribute to POAG risk. However, the APOE -219G carriers tended to have later-onset POAG.

Glaucoma screening: current trends, economic issues, technology, and challenges

PURPOSE OF REVIEW

Glaucoma is one of the leading causes of irreversible blindness worldwide. Early glaucoma detection and treatment are currently the only known methods for preventing blindness and low vision resulting from this frequently asymptomatic disease.

RECENT FINDINGS

New technologies for detecting early glaucomatous damage are important in diagnosing optic nerve disease, not only in community screening settings but also in clinics. Imaging of the optic nerve head and macula and retinal nerve fiber layer analysis can provide quick, automated, and quantitative measurements in agreement with clinical estimates of optic disc structure and visual function. In the area of perimetry, frequency-doubling technology is a promising and feasible mass-screening method with reasonable sensitivity for detecting visual field loss. Central corneal thickness has emerged as a new risk factor for the development and progression of glaucoma, thereby complicating the role of tonometry and measurement of intraocular pressure as screening parameters for glaucoma. Along with technological advances, strides are also being made with public policy and legislative efforts to bring glaucoma onto the national and global health care agenda. These initiatives incorporate vision-screening goals into national disease prevention programs emphasizing the need for early glaucoma detection and treatment.

SUMMARY

Glaucoma awareness needs to be increased through better education, and compliance with follow-up care needs to be improved to decrease the economic and social costs from glaucoma. In addition, screening models need to be developed that will be effective in developing countries where the risk of blindness from glaucoma is highest.

Confirmation of the adult-onset primary open angle glaucoma locus GLC1B at 2cen-q13 in an Australian family

Primary open-angle glaucoma (POAG) is genetically heterogeneous, with 6 named POAG loci GLC1A-F mapped and genes myocilin (MYOC) and optineurin (OPTN) identified at 2 of the loci. Using penetrance-model-free methods, we screened the POAG loci GLC1A-F in an extended Australian pedigree, using 3-5 markers within each locus. p values of less than 0.05 were obtained empirically using SimWalk2 and exactly using Genehunter for 2 markers within the GLC1B region on chromosome 2. Fine mapping of this region produced p values of 0.01 or less at 5 markers flanked by D2S1897 and D2S2269. The 9 cM haplotype of interest overlaps the original GLC1B region. These results provide supportive evidence for the GLC1B locus on chromosome 2cen-q13 and verify the existence of POAG susceptibility gene in this region, increasing the likelihood of gene identification.

Gene mapping for primary open angle glaucoma

Primary open angle glaucoma (POAG) is a leading cause of visual impairment and blindness worldwide. To date, at least 20 genetic loci for POAG have been reported. Only 3 causative genes are identified from these loci: myocilin (MYOC), optineurin (OPTN) and WD repeat domain 36 (WDR36), which together account for less than 10% of POAG. Only a portion of POAG follows Mendelian inheritance, and a considerable fraction results from a large number of variants in several genes, each contributing small effects. Over the past 10 years, there has been vigorous research on mapping the POAG genes. The main technological approaches are functional cloning, family linkage analysis, genome-wide scan, case-control association study, and microarray analysis. Association studies found 16 genes related to POAG, but reports on glaucoma-causing effects of these genes are conflicting. Ten microarray gene expression studies related to POAG have been published. A number of genes potentially related to POAG have been identified, and they provide a good resource to select candidate genes for mutation analysis in association studies. While linkage studies remain a mainstay, the current trend is to use genome-wide association studies to map genes for POAG. This review gives an overview of the efforts in the past decade to identify the POAG genes through linkage studies, genome-wide scans, case-control association studies and microarray studies. In the near future such comprehensive studies are expected to greatly advance our understanding of the genetic basis of POAG and provide information for effective glaucoma therapy.

Analysis of rare variants and common haplotypes in the optineurin gene in Swedish glaucoma cases

OBJECTIVE

Glaucoma, a leading cause of blindness in the world, is characterized by neuropathy of the retinal ganglion cells and the optic nerve. Recently, sequence alterations in the optineurin gene were shown to be associated with the disease in families with primarily normal tension glaucoma.

METHODS

In the present study, 200 patients with primary open-angle glaucoma, 200 patients with exfoliative glaucoma, and 200 matched controls were tested for alterations in the coding sequences using denaturing high-performance liquid chromatography and sequencing. In addition, single nucleotide polymorphisms distributed throughout the gene were typed and haplotypes were constructed.

RESULTS

No disease-causing alterations were found in either of the patient cohorts. The risk-associated allele M98K was found in equal amounts in both patients and controls. Analysis of haplotype frequencies and distribution revealed high haplotype diversity but no differences between patients and controls.

CONCLUSION

These experiments show no association between optineurin and our Swedish cohorts of high-pressure glaucoma cases, either in coding sequence or in haplotype frequency and distribution.

COMPLEX GENETICS OF GLAUCOMA SUSCEPTIBILITY

Glaucoma describes a group of diseases that kill retinal ganglion cells. There are different types of glaucoma, and each appears to be genetically heterogeneous. Different glaucoma genes have been identified, but these genes account for only a small proportion of glaucoma. Most glaucoma cases appear to be multifactorial, and are likely affected by multiple interacting loci. A number of genetic susceptibility factors have been suggested to contribute to glaucoma. These factors fit into two broad groups, those affecting intraocular pressure and those important in modulating retinal ganglion cell viability. Defining the complex genetics of glaucoma will require significant further study of the human disease and animal models. Genetic approaches are essential and will be enhanced by recently developed genomic and proteomic technologies. These technologies will provide valuable clues about pathogenesis for subsequent testing. In this review, we focus on endogenous genetic susceptibility factors and on how experimental studies will be valuable for dissecting the multifactorial complexity of their interactions.

Evidence for a novel glaucoma locus at chromosome 3p21-22

Primary open-angle glaucoma (POAG) is one of the leading causes of blindness in the world. It is a clinically variable group of diseases with the majority of cases presenting as the late onset adult type. Several chromosomal loci have been implicated in disease aetiology, but causal mutations have only been identified in a small proportion of glaucoma. We have previously described a large six-generation Tasmanian family with POAG exhibiting genetic heterogeneity. In this family, approximately one third of affected individuals presented with a glutamine-368-STOP (Q368STOP) mutation in the myocilin gene. We now use a Markov Chain Monte Carlo (MCMC) method to identify a second disease region in this family on the short arm of chromosome 3. This disease locus was initially mapped to the marker D3S1298 and a subsequent minimum disease region of 9 cM between markers D3S1298 and D3S1289 was identified through additional mapping. The region did not overlap with any previously described locus for POAG. Using a multiplicative relative risk model, we identified a positive association between this region and the Q368STOP mutation of myocilin on chromosome 1 in affected individuals. These findings provide evidence of a new autosomal dominant glaucoma locus on the short arm of chromosome 3.