Glaucoma Inheritance Study Research Articles

Myocilin Gene Gln368Ter Variant Penetrance and Association With Glaucoma in Population-Based and Registry-Based Studies

The p.Gln368Ter (rs74315329) risk allele in the myocilin gene (MYOC) was initially reported to have high penetrance in glaucoma registry-based studies, but much lower estimates were recently obtained from population-based studies. We investigated this disparity using data from Australia and the United Kingdom. To examine the penetrance and effect size of the MYOC p.Gln368Ter variant with glaucoma and ocular hypertension (OHT). This cross-sectional study within the UK Biobank (UKBB) included participants of white British ancestry. Glaucoma cases were defined by International Classification of Diseases, Ninth Revision (ICD-9) and Tenth Revision (ICD-10) diagnoses and self-reported questionnaires. Carriers of the MYOC p.Gln368Ter variant were identified using genotype imputation from arrays. In contrast, 2 Australian registry-based studies, the Australian and New Zealand Registry of Advanced Glaucoma and the Glaucoma Inheritance Study in Tasmania, ascertained glaucoma cases referred by eye care clinicians, with historic control participants recruited from other Australian studies. Samples were either directly sequenced or had genotypes determined by imputation (for the Australian registry and historic control participants). Recruitment to the UKBB occurred between 2006 and 2010, and data analysis occurred from September 2017 to July 2018. The penetrance and odds ratio (OR) were estimated for the MYOC p.Gln368Ter variants in participants with glaucoma and OHT. A total of 411 337 UKBB participants of white British ancestry (mean [SD] age, 56.6 [8.0] years) were included, plus 3071 Australian registry and 6750 historic control participants. In the UKBB, the minor allele frequency of the MYOC p.Gln368Ter variant was 1 in 786 individuals (0.13%). The odds ratio of p.Gln368Ter in patients with primary open-angle glaucoma (POAG) was 6.76 (95% CI, 4.05-11.29); glaucoma (POAG, self-reported glaucoma, and unspecified glaucoma), 4.40 (95% CI, 3.38-5.71); OHT, 3.56 (95% CI, 2.53-4.92); and OHT and glaucoma combined, 4.18 (95% CI, 3.05-5.67). The penetrance of the MYOC p.Gln368Ter variant was 7.6% in patients with glaucoma, 24.3% in patients with OHT, and 30.8% in patients with OHT and glaucoma combined. In the Australian registry studies, the odds of MYOC p.Gln368Ter variant were 12.16 (95% CI, 6.34-24.97) in patients with advanced glaucoma and 3.97 (95% CI, 1.55-9.75) in those with nonadvanced glaucoma; the penetrance of glaucoma was 56.1%, and penetrance in those considered to have glaucoma or be glaucoma suspects was 69.5%. The MYOC p.Gln368Ter variant confers a very high-risk effect size for advanced glaucoma; the risk is lower in nonadvanced glaucoma and OHT. In the general population sample, approximately 50% of MYOC p.Gln368Ter carriers 65 years and older had glaucoma or OHT, with higher prevalence in the Australian registry studies.

Genetic Association at the 9p21 Glaucoma Locus Contributes to Sex Bias in Normal-Tension Glaucoma.

Many genome-wide association studies have identified common single nucleotide polymorphisms (SNPs) at the 9p21 glaucoma locus (CDKN2B/CDKN2B-AS1) to be significantly associated with primary open-angle glaucoma (POAG), with association being stronger in normal tension glaucoma (NTG) and advanced glaucoma. We aimed to determine whether any observed differences in genetic association at the 9p21 locus are influenced by sex. Sex was assessed as a risk factor for POAG for 2241 glaucoma participants from the Australian and New Zealand Registry of Advanced Glaucoma, the Glaucoma Inheritance Study in Tasmania, and the Flinders Medical Centre. A total of 3176 controls were drawn from the Blue Mountains Eye Study and South Australia: 1523 advanced POAG and 718 nonadvanced POAG cases were genotyped along with 3176 controls. We selected 13 SNPs at the 9p21 locus, and association results were subanalyszd by sex for high-tension glaucoma (HTG) and NTG. Odds ratios (ORs) between sexes were compared. A sex bias was present within advanced NTG cases (57.1% female versus 42.9% male, P = 0.0026). In all POAG cases, the strongest associated SNP at 9p21 was rs1063192 (OR, 1.43; P = 4 × 10-18). This association was stronger in females (OR, 1.5; P = 5 × 10-13) than in males (OR, 1.35; P = 7 × 10-7), with a statistically significant difference in female to male OR comparison (P = 1.0 × 10-2). An NTG to HTG subanalysis yielded statistically significant results only in females (OR, 1.63; P = 1.5 × 10-4) but not in males (OR, 1.15; P = 2.8 × 10-1), with a statistically significant difference in female to male OR comparison (P = 1.4 × 10-4). This study demonstrated that female sex is a risk factor for developing advanced NTG. The stronger genetic signals at the 9p21 locus among females may contribute at least in part to the observed sex bias for NTG.

Systemic disease associations of familial and sporadic glaucoma: the Glaucoma Inheritance Study in Tasmania

This aim of this study was to compare the prevalence of various disease-associated and potentially modifiable risk factors between people with familial and sporadic forms of primary open angle glaucoma (OAG). A cross-sectional, retrospective study design was utilized. A detailed questionnaire enquiring about knowledge of family history, demographic data, current medications, and medical history of systemic disorders was administered. Where possible, living relatives were examined for signs of OAG. A total of 3,800 potential patients with OAG were identified, of whom 2062 were examined. One thousand twelve (59.5%) subjects were found to have familial OAG, and 688 (40.5%) subjects had no known or identified relative with OAG (sporadic glaucoma). One thousand forty-two unaffected family members examined. A past history of migraine was found more often with familial OAG (OR: 1.67 95% CI: 1.15-2.42). This effect was primarily driven by patients who had a first-degree relative also affected by OAG. Following adjustment for male gender and the age at review, the presence of atherosclerosis was also found to be more common in patients with familial glaucoma than in people with sporadic disease (OR: 1.42 95% CI: 1.05-1.92). No significant difference in the prevalence of hypertension, Raynaud's phenomenon, diabetes mellitus or thyroid disease was identified. Patients with a known relative affected by OAG were statistically significantly more likely to have a past history for migraine or presence of atherosclerosis compared to people with no known affected relative. An understanding of such differences and systemic comorbidities will be useful for further work investigating the underlying molecular mechanisms of this disease.

Mortality in primary open-angle glaucoma: ‘two cupped discs and a funeral’

The aim of this study was to investigate the causes of mortality in individuals with open-angle glaucoma (OAG). All-cause mortality data from the Registry of Births, Deaths and Marriages for the Australian state of Tasmania, for all people who were at least 40 years of age at the time of death, were classified using International Classification of Diseases-10 guidelines. This information was cross-referenced to identify participants in the Glaucoma Inheritance Study in Tasmania (GIST) who had died. Contingency tables were used for crude analysis and then models were constructed, adjusting for age at death as well as gender. Between 1996 and 2005, a total of 33 879 deaths were recorded. Data were unavailable for 4868 (14.4%) people. The mean age at death for the study sample was 78.4+/-11.5 (range 41-109) years. Of those cases known to have OAG by their participation in GIST (n=2409), full mortality data were available for 741 (92.0%). Following adjustment for the age at death and male gender, the odds ratio for death due to ischaemic heart disease in people with OAG compared to the general population not known to have OAG was significant (OR=1.30, 95% CI: 1.08-1.56; P=0.006). Crude analysis revealed that there were significantly fewer people with OAG who died due to metastatic cancer (P<0.001); however, this did not remain significant following adjustment for age and gender. The pathoaetiological relationship between OAG and ischaemic heart disease is unclear and requires further investigation. Increased awareness of the association between cardiovascular disease and OAG is warranted.

Primary open angle glaucoma in subjects harbouring the predictedGLC1Lhaplotype reveals a normotensive phenotype

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. 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. 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. 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.

Gillies Lecture: Dissecting glaucoma: understanding the molecular risk factors

WE Gillies was a major contributor to research in glaucoma, notably pseuodexfoliation (XFS), as well as strabismus, particularly in relation to axial length (AL). The latter work involved breaking down the geometry of the eye to its basic components and using the measured AL to tailor the amount of strabismus surgery required. Similarly, the search for glaucoma genes requires us to break down glaucoma into its component measures and associated risk factors. Over the last 14 years, our data from the Glaucoma Inheritance Study in Tasmania have shown the following: that a family history is present in 60% of glaucoma cases; that 27% of members of large glaucoma families were unaware of their family history of glaucoma; and that familial glaucoma is more severe than sporadic glaucoma. Myocilin mutations account for 3% of cases of primary open angle glaucoma. Some genotype-phenotype correlations have been identified. Notably, with respect to earlier age of onset, higher maximum recorded intraocular pressure and need for surgery, the Gln368Stop mutation confers mild risk, Thr377Met and Gly252Arg mutations intermediate risk, and the Pro370Leu mutation severe risk. To identify the other genes associated with glaucoma, we have examined normal twins in the Twins Eye Study to determine the heritability of parameters that are abnormal in glaucoma - intraocular pressure and cup-to-disc ratio and confounding factors for glaucoma such as central corneal thickness, disc area, refraction and AL. We have identified high heritabilities for all of these as well as a gene locus associated with AL on chromosome 5. Recently, the LOXL1 gene was associated with XFS. Identification of further genes will improve our understanding of glaucoma and allow cascade genetic screening.

How significant is a family history of glaucoma? Experience from the Glaucoma Inheritance Study in Tasmania

To determine what proportion of primary open angle glaucoma (POAG) in Tasmania, Australia is familial. Between 1994 and 1996 an audit of Tasmanian patients diagnosed with glaucoma was performed. Identified probands along with their family members were invited to participate. Family history of POAG was noted and pedigrees constructed. Each participant underwent a detailed examination, including visual acuity, intraocular pressure measurement, gonioscopy, optic disc assessment and visual field testing. Participants were classified as normal, suspect or POAG. Data from 467 participants in the Twins Eye Study in Tasmania (TEST) were used as a reference for the general population. Of 2062 participants examined, 1700 were classified as POAG. A total of 1014 participants (59.6%) belonged to families in which other members were affected (familial glaucoma). Six hundred and fifty-six of these 1014 familial cases (64.8%) had a first-degree relative affected. The number of affected members in the family groups varied from two to 29. Six hundred and eighty-eight participants had no known family history of POAG (sporadic glaucoma). There were significantly more POAG patients with a family history of POAG compared to the TEST population (chi2 = 161.81, P < 0.0001), and for a person with POAG the odds ratio of having a positive family history was 4.1 (95% confidence interval: 3.2-5.2). Approximately 60% of POAG in Tasmania is familial. This percentage is higher than most previous reports of familial glaucoma and emphasizes the importance of genetics in POAG, with major implications for screening and future research.

No Maternally Inherited Diabetes and Deafness Mutations in a Sample of 193 Tasmanian Diabetics with Glaucoma

We tested the hypothesis that the presence of the mitochondrial 3243 A-G mutation responsible for maternally inherited diabetes and deafness (MIDD)1 may partly explain the association between glaucoma and diabetes mellitus. The 3243 AG mutation has been estimated to be responsible for 1–3% of the non-insulin-dependent diabetes mellitus cases in Northern Europe2 and approximately 1% in Japan.3 We tested 193 DNA samples collected from Tasmanians with both diseases recruited through the Glaucoma Inheritance Study in Tasmania.4 No cases with the 3243 A-G mutation were detected.

A Glaucoma Case-control Study of the WDR36 Gene D658G Sequence Variant

To investigate in Australian patients with glaucoma and normal controls the prevalence and associated phenotype of the WDR36 D658G mutation, which has previously been suggested to be a disease-causing mutation in pedigrees with primary open-angle glaucoma (POAG). Case-control study. Two hundred forty-nine individuals with POAG and 217 age-matched control subjects were recruited through the Glaucoma Inheritance Study in Tasmania, Australia. Genomic DNA was amplified by polymerase chain reaction by intronic primers. The presence of the D658G variant was detected by BglI restriction enzyme digestion. The D658G variant was identified in four POAG cases (1.6%) and four control subjects (1.8%) (chi(2) = 0.04, P = .84). No control subject with the variant had a family history of glaucoma. The WDR36 D658G is a neutral variant in the Australian population. Further populations should be carefully assessed for this variant before concluding that WDR36 is a glaucoma gene.

Disease Severity of Familial Glaucoma Compared With Sporadic Glaucoma

To determine whether there is a difference in disease severity between familial and sporadic primary open-angle glaucoma (POAG). A cross-sectional study design compared the distribution of Glaucoma Inheritance Study in Tasmania (GIST) severity scores of patients with genealogically confirmed familial POAG and those with sporadic POAG. The GIST severity scores provide a combined weighting of glaucoma severity based on findings from visual field defects and optic disc analysis, with and without intraocular pressure. A Poisson regression analysis, t test, and chi(2) tests were performed. One thousand twelve (59.5%) of 1700 subjects had familial glaucoma. The mean +/- SD age at examination was greater in the sporadic POAG group compared with the familial group (72.6 +/- 10.3 years vs 70.6 +/- 12.6 years; P = .001). The family group was significantly younger at diagnosis than the sporadic group (mean +/- SD, 61.4 +/- 13.0 years vs 64.0 +/- 12.6 years; P<.001). The GIST severity scores were significantly skewed toward greater disease severity in the familial group compared with the sporadic group (P<.001). Identifying individuals at risk of severe POAG will be more successful if screening programs are developed with appropriate weighting toward those with a positive family history of the disease.

Glaucoma phenotype in pedigrees with the myocilin Thr377Met mutation.

To investigate the phenotype and age-related penetrance of primary open-angle glaucoma (POAG) in Australian families with the myocilin mutation Thr377Met. Cross-sectional genetic study. Four unrelated pedigrees carrying the Thr377Met mutation were ascertained from more than 2000 consecutive cases of POAG in the Glaucoma Inheritance Study in Tasmania and from families with glaucoma referred to the study from throughout Australia. Index cases and available family members were examined for signs of glaucoma, and the presence of the GLC1A Thr377Met mutation was ascertained by single-strand conformation polymorphism analysis and subsequent direct sequencing. From the 4 pedigrees carrying the Thr377Met mutation, 23 individuals with either ocular hypertension (OHT) or POAG were found, with a mean +/- SD age at diagnosis of 41.2 +/- 11.5 years, and a mean peak intraocular pressure of 31.7 +/- 9.9 mm Hg. A further 9 mutation carriers older than 18 years were studied who as yet showed no signs of OHT or POAG (6 of these 9 were younger than 30 years). A single individual with POAG was identified who did not carry the Thr377Met mutation. For Thr377Met carriers, age-related penetrance for OHT or POAG was 88% at age 30 years. A positive family history of POAG was present for 3 of the 4 index cases. Thirteen (57%) of the 23 Thr377Met carriers with OHT or POAG had undergone glaucoma drainage surgery. Although the glaucoma in these families appears to be pressure dependent, 2 individuals showed optic disc cupping before detected elevation in intraocular pressure. One family was of British origin, with a different background haplotype from the other 3 families from Greece or Macedonia, who shared a common haplotype. The GLC1A Thr377Met mutation is associated with POAG that, in the pedigrees studied, had a younger age at onset and higher peak intraocular pressure than in pedigrees with the more common Gln368STOP mutation. In addition, patients with glaucoma with the Thr377Met mutation were more likely to have undergone glaucoma drainage surgery.

Evidence for genetic heterogeneity within eight glaucoma families, with the GLC1A Gln368STOP mutation being an important phenotypic modifier.

To investigate the phenotype and age-related penetrance of primary open-angle glaucoma (POAG) in Australian families with the most common Myocilin mutation (Gln368STOP). Cross-sectional genetic study. Eight pedigrees carrying the Gln368STOP mutation were ascertained from 1730 consecutive cases of POAG in the Glaucoma Inheritance Study in Tasmania. Index cases and available family members were examined for signs of glaucoma, and the presence of the GLC1A Gln368STOP mutation was ascertained by single-strand conformation polymorphism analysis and subsequent direct sequencing. From the eight pedigrees, 29 Gln368STOP mutation-carrying individuals with either ocular hypertension (OHT) or POAG were found, with a mean age at diagnosis of 52.4 +/- 12.9 years and a mean peak intraocular pressure (IOP) of 28.4 +/- 4.7 mmHg. A further 11 mutation carriers older than 40 years have been studied, who as yet show no signs of OHT or POAG. Within the 8 pedigrees, a further 31 individuals with OHT or POAG were identified who did not carry the Gln368STOP mutation. For these individuals the mean age at diagnosis was higher (62.3 +/- 13.7 years, P < 0.01), and the mean peak IOP was lower (25.4 +/- 6.4 mmHg, P = 0.01). For Gln368STOP carriers, age-related penetrance for OHT or POAG was 72% at age 40 years and 82% at age 65 years. A positive family history of POAG was present in all index cases. Five of the eight pedigrees had a positive family history on both maternal and paternal sides. Seven of the eight pedigrees had one or more individuals with POAG who did not carry the mutation. Eight of the 29 Gln368STOP carriers with OHT or POAG had undergone trabeculectomy. The GLC1A Gln368STOP mutation is associated with POAG, which in the pedigrees studied is of a younger age of onset and higher peak IOP than non-mutation glaucoma cases. In addition, Gln368STOP mutation glaucoma cases were more likely to have undergone glaucoma drainage surgery. We have not observed simple autosomal dominant inheritance patterns for POAG in these pedigrees. Other factors, as yet uncharacterized, are involved in expression of the POAG phenotype in Gln368STOP pedigrees.

The problem of overlapping glaucoma families in the Glaucoma Inheritance Study in Tasmania (GIST).

The Glaucoma Inheritance Study in Tasmania (GIST) is a population survey of Australia's island state, Tasmania (population 450,000). Its aim is to find families with autosomal dominant, adult-onset, primary open angle glaucoma (POAG) suitable for genetic linkage analysis. POAG is relatively common, affecting around 3% of the Australian population. By finding the large families with POAG and identifying all the descendants in a captive population, it is possible that there may be overlap of different glaucoma pedigrees. Three of the first thirteen families in the study were composed of overlapping pedigrees. In one GIST family, GTas3, there has been intermarriage with other pedigrees with glaucoma on five occasions. The possibility of multiple genotypes was also reinforced by the inability to determine a single glaucoma phenotype in this family. When finding large families of POAG for linkage analysis, researchers must be aware of the risk of affected individuals inheriting their gene from the alternate parent. Thus, the alternate parents or their families must be examined, especially if the phenotype is atypical for the rest of the family.

The 'GIST' score: ranking glaucoma for genetic studies. Glaucoma Inheritance Study of Tasmania.

The 'GIST' score was developed to facilitate linkage analysis of adult-onset primary open angle glaucoma (POAG) pedigrees in the Glaucoma Inheritance Study of Tasmania (GIST). Previous genetic linkage studies on juvenile open angle glaucoma pedigrees have relied upon an analysis of definitely affected individuals using the 'single best diagnosis' convention. Studies of adult-onset POAG have been complicated by limited numbers of unequivocally affected members identified even in very large pedigrees due to the later onset of the disease. Many members of the pedigree may have equivocal clinical features or are too young to show signs of the disease. The 'GIST score' is a numeric value between zero and one where zero is clinical certainty of absence of the disease and one is the definitive diagnosis of POAG. The score is developed by assigning relative weighting to key clinical features which results in a 'pedigee probability' of the diagnosis being present or absent in a member of a pedigree. Ranking of borderline and unaffected glaucoma subjects allows the laboratory more flexibility in the use of the members of the pedigree for linkage analysis. The score is not intended to have clinical usefulness in management of glaucoma.