Higher prevalence of myocilin mutations in advanced glaucoma in comparison with less advanced disease in an Australasian disease registry

Genetics and Glaucoma: the state of the art

Glaucoma is the second leading cause of irreversible blindness worldwide. Although genetic background contributes differently to rare early-onset glaucoma (before age 40) or common adult-onset glaucoma, it is now considered an important factor in all major forms of the disease. Genetic and genomic studies, including GWAS, are contributing to identifying novel loci associated with glaucoma or to endophenotypes across ancestries to enrich the knowledge about glaucoma genetic susceptibility. Moreover, new high-throughput functional genomics contributes to defining the relevance of genetic results in the biological pathways and processes involved in glaucoma pathogenesis. Such studies are expected to advance significantly our understanding of glaucoma's genetic basis and provide new druggable targets to treat glaucoma. This review gives an overview of the role of genetics in the pathogenesis or risk of glaucoma.

Analysis of glaucoma genes in Finnish patients with juvenile open-angle glaucoma

PURPOSE

To identify germline variants in myocilin (MYOC) and other known monogenic glaucoma genes in Finnish patients with juvenile open-angle glaucoma (JOAG).

METHODS

Finnish patients with JOAG treated between 2010 and 2018 at the Department of Ophthalmology, Helsinki University Hospital, Finland, were enrolled. We sequenced all exonic regions and flanking splice sites of MYOC for five patients and one healthy relative using Sanger sequencing. In 48 patients, we performed exome sequencing to identify variants also in 28 other glaucoma-related genes.

RESULTS

Fifty-three individuals with JOAG from 50 pedigrees, and one healthy relative, participated. The mean age at diagnosis was 30.8 years [SD 7.6; range 11 to 39]. Five probands had probably pathogenic variants in MYOC: c.1102C>T p.(Gln368Ter), c.1109C>T p.(Pro370Leu), c.1130C>T p.(Thr377Met), c.1132G>A p.(Asp378Asn) and c.1456C>T p.(Leu486Phe). Four of these patients had a family history of dominantly inherited JOAG. The frequency of MYOC variants was 10% (5 of 50 families). One patient and his mother with JOAG had a novel loss-of-function variant in the FOXC1 gene, c.366G>A p.(Trp122Ter). A patient with sporadic JOAG had a homozygous likely pathogenic variant in the LTBP2 gene, c.3938G>A p.(Cys1313Tyr). The genetic variants explained 14% (7 out of 50 families; 95% CI, 6%-23%) of JOAG in our cohort.

CONCLUSIONS

The frequency of pathogenic variants in previously known glaucoma-associated genes is low in Finnish patients with JOAG. Because of the distinct genetic background of Finns, it might be possible to identify novel glaucoma genes through our JOAG series in the future.

Specifications of the ACMG/AMP variant curation guidelines for myocilin: Recommendations from the clingen glaucoma expert panel

The standardization of variant curation criteria is essential for accurate interpretation of genetic results and clinical care of patients. The variant curation guidelines developed by the American College of Medical Genetics and Genomics (ACMG) and the Association for Molecular Pathology (AMP) in 2015 are widely used but are not gene specific. To address this issue, the Clinical Genome Resource (ClinGen) Variant Curation Expert Panels (VCEP) have been tasked with developing gene-specific variant curation guidelines. The Glaucoma VCEP was created to develop rule specifications for genes associated with primary glaucoma, including myocilin (MYOC), the most common cause of Mendelian glaucoma. Of the 28 ACMG/AMP criteria, the Glaucoma VCEP adapted 15 rules to MYOC and determined 13 rules not applicable. Key specifications included determining minor allele frequency thresholds, developing an approach to counting probands and segregations, and reviewing functional assays. The rules were piloted on 81 variants and led to a change in classification in 40% of those that were classified in ClinVar, with functional evidence influencing the classification of 18 variants. The standardized variant curation guidelines for MYOC provide a framework for the consistent application of the rules between laboratories, to improve MYOC genetic testing in the management of glaucoma.

Case Report: Reversal and subsequent return of optic disc cupping in a myocilin (MYOC) gene-associated severe Juvenile Open-Angle Glaucoma (JOAG) patient

To our knowledge, this case report describes the first instance of reversal of glaucomatous optic nerve cupping in a young adult with a rare form of juvenile open-angle glaucoma (JOAG) associated with a novel variant of the myocilin gene (MYOC). This 25-year-old woman with severe-stage MYOC-associated JOAG presented with blurry vision and intermittent pain in her left eye. She had a strong family history of glaucoma in multiple first-degree relatives with an identified novel variant of MYOC. Examination revealed intraocular pressures (IOPs) of 10 mmHg OD and 46 mmHg OS, with cup-to-disc ratios of 0.90 and 0.80. The patient experienced substantial reversal of optic disc cupping OS following dramatic IOP reduction with trabeculectomy, and subsequently experienced a return of cupping after an IOP spike 15 months postoperatively. The reversal of cupping did not correspond to any changes in the patient's visual field. After an initial decrease in retinal nerve fiber layer (RNFL) thickness, RNFL remained stable for over 2 years after trabeculectomy as seen on Optical Coherence Tomography (OCT). This case suggests reversal of cupping can occur well into adulthood in a MYOC-associated JOAG patient, and it demonstrates the potential bidirectionality of this phenomenon. Moreover, it suggests that these structural changes may not correspond to any functional changes in visual fields or RNFL thickness.

Structure‒function‒pathogenicity analysis of C-terminal myocilin missense variants based on experiments and 3D models

MYOC is a common pathogenic gene for primary open-angle glaucoma and encodes the protein named myocilin. Multiple MYOC variations have been found, with different clinical significance. However, the pathogenesis of glaucoma induced by MYOC mutations has not been fully clarified. Here, we analyze the molecular and cellular biological differences caused by multiple variant myocilins, including protein secretion characteristics, structural changes, subcellular localization, cellular autophagic activity and oxidative stress. Denaturing and nondenaturing electrophoresis showed myocilin to be a secreted protein with the tendency to self-oligomerize. The full-length myocilin and its C-terminal cleavage fragment are secreted. Secretion analysis of 23 variant myocilins indicated that secretion defects are closely related to the pathogenicity of MYOC variants. Structural analysis showed that the alteration of steric clash is associated with the secretion characteristics and pathogenicity of myocilin variants. Immunocytochemistry results demonstrated that mutated myocilins are retained in the endoplasmic reticulum and disrupt autophagy. MTT assay, MitoTracker staining, and DCFH-DA staining showed increased oxidative injury in cells expressing MYOC mutants. Taken together, MYOC mutations are able to induce cell dysfunction via secretion defects and intracellular accumulation resulting from steric clash alterations.

Age at Glaucoma Diagnosis in Germline Myocilin Mutation Patients: Associations with Polymorphisms in Protein Stabilities

Glaucoma is the leading cause of irreversible blindness worldwide, with elevated intraocular pressure (IOP) as the only known modifiable risk factor. Trabecular meshwork (TM)-inducible myocilin (the MYOC gene) was the first to be identified and linked to juvenile and primary open-angle glaucoma. It has been suggested that mutations in the MYOC gene and the aggregation of mutant myocilin in the endoplasmic reticulum (ER) of TM may cause ER stress, resulting in a reduced outflow of aqueous humor and an increase in IOP. We selected 20 MYOC mutations with experimentally determined melting temperatures of mutated myocilin proteins. We included 40 published studies with at least one glaucoma patient with one of these 20 MYOC mutations and information on age at glaucoma diagnosis. Based on data from 458 patients, we found that a statistically significant but weak correlation was present between age and melting temperature based on various assumptions for age. We therefore conclude that genetic analysis of MYOC mutations alone cannot be used to accurately predict age at glaucoma diagnosis. However, it might be an important prognostic factor combined with other clinical factors for critical and early detection of glaucoma.

Prevalence of MYOC risk variants for glaucoma in different populations

PURPOSE

To assess the clinical relevance of myocilin (MYOC) gene variants as risk factors for glaucoma in literature and to estimate their prevalence in different populations.

METHODS

We reviewed the literature for published MYOC variants in glaucoma patients and estimated their prevalence in general population using gnomAD and BRAVO databases. We used several bioinformatics tools and the criteria of the American College of Medical Genetics and Genomics (ACMG) to assess the pathogenicity of the variants. We evaluated the carrier frequency of the variants in gnomAD, including its subpopulations.

RESULTS

We found 13 missense and 5 loss-of-function (LOF) reported variants in MYOC that were both probable pathogenic or risk variants and listed in gnomAD. Six likely pathogenic missense variants were p.(Cys25Arg), p.(Gln48His), p.(Gly326Ser), p.(Thr353Ile), p.(Thr377Met) and p.(Gly399Val). They were most prevalent in East and South Asia (frequency, 0.92% and 0.81%, respectively). The most common missense variants were p.(Thr353Ile) (0.91% in East Asia) and p.(Gln48His) (0.79% in South Asia). Five LOF variants were p.(Arg46Ter), p.(Arg91Ter), p.(Arg272Ter), p.(Gln368Ter) and p.(Tyr453MetfsTer11). We considered these glaucoma risk variants. They were most prevalent in the East Asian and the Finnish population (0.93% and 0.33%, respectively).

CONCLUSION

Pathogenic MYOC variants appear to be population-associated. Our results highlight allelic heterogeneity of MYOC variants in open-angle glaucoma. Many of the probable pathogenic variants are over-represented in some of the populations causing doubt of their status as monogenic disease-causing variants.

Association of the MYOC p.(Gln368Ter) Variant With Glaucoma in a Finnish Population

Importance

The c.1102C>T, p.(Gln368Ter) variant in the myocilin (MYOC) gene is a known risk allele for glaucoma. It is the most common MYOC risk variant for glaucoma among individuals of European ancestry, and its prevalence is highest in Finland. Furthermore, exfoliation syndrome has high prevalence in Scandinavia, making the Finnish population ideal to study the association of the variant with different types of glaucoma.

Objectives

To examine the association and penetrance of MYOC p.(Gln368Ter) (rs74315329) variant with different types of glaucoma in a Finnish population.

Design, Setting, and Participants

This genetic association study included individuals of Finnish ancestry in the FinnGen project. The participants were collected from Finnish biobanks, and the disease end points were defined using nationwide registries. The MYOC c.1102C>T variant was either directly genotyped or imputed with microarrays. Recruitment of samples to FinnGen was initiated in 2017, and data analysis was performed between December 2019 and May 2020.

Main Outcomes and Measures

The main outcomes were odds ratios (ORs) and penetrance with different types of glaucoma and in different age groups.

Results

A total of 218 792 individuals were included in this study (mean [SD] age 52.4 [17.5] years; 123 579 women [56.5%]), including 8591 (3.9%) with glaucoma, 3412 (1.6%) with primary open-angle glaucoma, 1515 (0.7%) with exfoliation glaucoma, 892 (0.4%) with normal-tension glaucoma, and 4766 (2.2%) with suspected glaucoma. The minor allele frequency of MYOC p.(Gln368Ter) was 0.28%. Individuals with the heterozygous variant had higher odds of primary open-angle glaucoma (OR, 3.36; 95% CI, 2.55-4.37), overall glaucoma (OR, 2.58; 95% CI, 2.12-3.13), suspected glaucoma (OR, 2.53; 95% CI, 1.93-3.26), exfoliation glaucoma (OR, 2.61; 95% CI, 1.60-4.02), and undergoing glaucoma-related operations (OR, 5.45; 95% CI, 2.95-9.28). The penetrance of heterozygous MYOC p.(Gln368Ter) was 5.2% in individuals with primary open-angle glaucoma, 9.6% in individuals with glaucoma, 5.4% in individuals with suspected glaucoma, and 1.9% in individuals with exfoliation glaucoma. There was no significant association with normal-tension glaucoma (OR, 1.69; 95% CI, 0.72-3.35).

Conclusions and Relevance

This genetic association study found that the MYOC p.(Gln368Ter) variant was associated with exfoliation glaucoma. The association with normal-tension glaucoma could not be replicated. These findings suggest that MYOC p.(Gln368Ter) was associated with open-angle glaucoma and exfoliation glaucoma in a Finnish population.

Childhood and Early Onset Glaucoma Classification and Genetic Profile in a Large Australasian Disease Registry

PURPOSE

To report the relative frequencies of childhood and early onset glaucoma subtypes and their genetic findings in a large single cohort.

DESIGN

Retrospective clinical and molecular study.

PARTICIPANTS

All individuals with childhood glaucoma (diagnosed 0 to <18 years) and early onset glaucoma (diagnosed 18 to <40 years) referred to a national disease registry.

METHODS

We retrospectively reviewed the referrals of all individuals with glaucoma diagnosed at <40 years of age recruited to the Australian and New Zealand Registry of Advanced Glaucoma (ANZRAG). Subtypes of glaucoma were determined using the Childhood Glaucoma Research Network (CGRN) classification system. DNA extracted from blood or saliva samples underwent sequencing of genes associated with glaucoma.

MAIN OUTCOME MEASURES

The phenotype and genotype distribution of glaucoma diagnosed at <40 years of age.

RESULTS

A total of 290 individuals (533 eyes) with childhood glaucoma and 370 individuals (686 eyes) with early onset glaucoma were referred to the ANZRAG. Primary glaucoma was the most prevalent condition in both cohorts. In the childhood cohort, 57.6% of individuals (167/290, 303 eyes) had primary congenital glaucoma (PCG), and 19.3% (56/290, 109 eyes) had juvenile open-angle glaucoma. Juvenile open-angle glaucoma constituted 73.2% of the early onset glaucoma cohort (271/370, 513 eyes). Genetic testing in probands resulted in a diagnostic yield of 24.7% (125/506) and a reclassification of glaucoma subtype in 10.4% of probands (13/125). The highest molecular diagnostic rate was achieved in probands with glaucoma associated with nonacquired ocular anomalies (56.5%). Biallelic variants in CYP1B1 (n = 29, 23.2%) and heterozygous variants in MYOC (n = 24, 19.2%) and FOXC1 (n = 21, 16.8%) were most commonly reported among probands with a molecular diagnosis. Biallelic CYP1B1 variants were reported in twice as many female individuals as male individuals with PCG (66.7% vs. 33.3%, P = 0.02).

CONCLUSIONS

We report on the largest cohort of individuals with childhood and early onset glaucoma from Australasia using the CGRN classification. Primary glaucoma was most prevalent. Genetic diagnoses ascertained in 24.7% of probands supported clinical diagnoses and genetic counseling. International collaborative efforts are required to identify further genes because the majority of individuals still lack a clear molecular diagnosis.

Bilateral Exudative Retinal Detachment in a Young Patient with Chronic Renal Failure

Introduction

Chronic renal failure (CRF) is a multi-systemic disease affecting different organ systems of the body. Ocular manifestations of chronic renal disease include squint, subconjunctival hemorrhage, vitreous hemorrhage, neovascular glaucoma, cataracts and retinal detachment. These result in visual impairment or blindness. In this article, a case of bilateral exudative retinal detachment (ERD) in a pediatric patient with CRF and hypertension is presented.

Methods

The patient is a 16-year-old girl with CRF, grade 3 hypertension, and bilateral ERD. Detailed ophthalmic evaluation including visual acuity, anterior and posterior segments evaluation with +78 DS super field lens and digital slit lamp, intraocular pressure (IOP) measurement using a non-contact tonometer. B-mode ocular and renal ultrasounds scan were done.

Results

With the management of systemic hypertension, and hemodialysis, a slight improvement of vision was noted but this was not sustained as renal replacement therapy was not continued due to financial constraints.

Conclusion

Ocular disturbances may be the pointer to renal compromise. There is a need for thorough systemic review in patients with ocular symptoms and ocular evaluation in all patients with CRF and hypertension.

Effects of caloric restriction on retinal aging and neurodegeneration

Glaucoma is the most common neurodegenerative cause of irreversible blindness worldwide. Restricted caloric regimens are an attractive approach for delaying the progression of neurodegenerative diseases. Here we review the current literature on the effects of caloric restriction on retinal neurons, under physiological and pathological conditions. We focused on autophagy as one of the mechanisms modulated by restricted caloric regimens and involved in the death of retinal ganglion cells (RGCs) over the course of glaucoma.

Myocilin Mutations in Patients With Normal-Tension Glaucoma

Importance

Mutations in the myocilin (MYOC) gene are the most common molecularly defined cause of primary open-angle glaucoma that typically occurs in patients with high intraocular pressures (IOP). One MYOC mutation, p.Gln368Ter, has been associated with as many as 1.6% of primary open-angle glaucoma cases that had a mean maximum recorded IOP of 30 mm Hg. However, to our knowledge, the role of the p.Gln368Ter mutation in patients with normal-tension glaucoma (NTG) with an IOP of 21 mm Hg or lower has not been investigated.

Objective

To evaluate the role of the p.Gln368Ter MYOC mutation in patients with NTG.

Design, Setting, and Participants

In this case-control study of the prevalence of the p.Gln368Ter mutation in patients with NTG, cohort 1 was composed of 772 patients with NTG and 2152 controls from the United States (Iowa, Minnesota, and New York) and England and cohort 2 was composed of 561 patients with NTG and 2606 controls from the Massachusetts Eye and Ear Infirmary and the NEIGHBORHOOD consortium. Genotyping was conducted using real-time polymerase chain reaction that was confirmed with Sanger sequencing, the imputation of genome-wide association study data, or an analysis of whole-exome sequence data. Data analysis occurred between April 2007 and April 2018.

Main Outcomes and Measures

Comparison of the frequency of the p.Gln368Ter MYOC mutation between NTG cases and controls with the Fisher exact test.

Results

Of 6091 total participants, 3346 (54.9%) were women and 5799 (95.2%) were white. We detected the p.Gln368Ter mutation in 7 of 772 patients with NTG (0.91%) and 7 of 2152 controls (0.33%) in cohort 1 (P = .03). In cohort 2, we detected the p.Gln368Ter mutation in 4 of 561 patients with NTG (0.71%) and 10 of 2606 controls (0.38%; P = .15). When the cohorts were analyzed as a group, the p.Gln368Ter mutation was associated with NTG (odds ratio, 2.3; 95% CI, 0.98-5.3; P = .04).

Conclusions and Relevance

In cohorts 1 and 2, the p.Gln368Ter mutation in MYOC was found in patients with IOPs that were 21 mm Hg or lower (NTG), although at a frequency that is lower than previously detected in patients with higher IOP. These data suggest that the p.Gln368Ter mutation may be associated with glaucoma in patients with normal IOPs as well as in patients with IOPs that are greater than 21 mm Hg.

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

Importance

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.

Objectives

To examine the penetrance and effect size of the MYOC p.Gln368Ter variant with glaucoma and ocular hypertension (OHT).

Design, Setting, and Participants

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.

Main Outcomes and Measures

The penetrance and odds ratio (OR) were estimated for the MYOC p.Gln368Ter variants in participants with glaucoma and OHT.

Results

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%.

Conclusions and Relevance

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.

Effects of Brimonidine and Timolol on the Progression of Visual Field Defects in Open-angle Glaucoma: A Single-center Randomized Trial

PRéCIS:: Instillation of brimonidine or timolol slowed visual field deterioration in patients with open-angle glaucoma; both brimonidine and timolol might improve the mean deviation (MD) slopes.

PURPOSE

The purpose of this study was to investigate and compare the effects of 0.1% brimonidine and 0.5% timolol on the progressing visual field defects in open-angle glaucoma.

PATIENTS AND METHODS

We evaluated 1 eye each of 68 glaucoma patients who were treated with at least 1 prostaglandin analog. Their baseline MD slopes were < -0.5 dB/y based on at least 5 Humphrey field analyzer measurements within 3 years. Eligible eyes were randomly assigned to brimonidine or timolol treatment groups and treatments were administered without the wash-out period. Clinical examinations were performed every 4 months for 2 years. We designated the MD slope as the primary endpoint.

RESULTS

Ultimately, 56 eyes (brimonidine:timolol=26:30) were included in the present study (mean age=65.2 y). Dropout rates of brimonidine and timolol treatment groups were 27.8% and 6.3%, respectively. There were no significant differences in baseline intraocular pressure or MD slopes between brimonidine and timolol groups (12.7 and 12.9 mm Hg, P=0.77, and -1.22 and -1.08 dB/y, P=0.43, respectively). Intraocular pressure decreased significantly in the brimonidine group at 4, 8, 12, and 16 months, and in the timolol group at 4 months, without significant differences between the drugs (P=0.20). MD slopes significantly improved in both groups (brimonidine: -0.38 dB/y, P<0.001; timolol: -0.52 dB/y, P=0.04). Furthermore, there was no significant difference between groups in the primary endpoint (P=0.59).

CONCLUSION

Brimonidine and timolol treatments improved MD slopes in open-angle glaucoma.

Clinical Registries in Ophthalmology

TOPIC

Clinical registries in ophthalmology.

CLINICAL RELEVANCE

In recent years, advancements in digital technology and increasing use of electronic medical records in health systems have led to the dramatic growth in large clinical data sets. Clinical data registries are organized systems that collect data on patients diagnosed with a disease or condition or who undergo a certain procedure.

METHODS

A search of the PUBMED database was conducted in January 2018 for clinical registries in ophthalmology.

RESULTS

Ninety-seven clinical eye registries were found, with significant growth in numbers in the last 4 decades. The most common conditions captured were blindness or low vision, corneal transplantation, glaucoma, and cataract surgery. Most registries originate in the European region, North America, and Australia. Nine registries had multinational coverage, whereas 48 were national registries. As the numbers and scope of clinical registries have expanded, valuable observational data have been used to study real-world clinical outcomes in healthcare quality measurement and improvement and to develop new guidelines and standards. Pertinent areas of its use include studying treatments and outcomes in cataract surgery, corneal transplantation, and macular degeneration.

CONCLUSIONS

The use of clinical registries for quality improvement and research has grown significantly in the last few decades, and this trend will continue as information technology infrastructures develop.

Binding of a glaucoma-associated myocilin variant to the αB-crystallin chaperone impedes protein clearance in trabecular meshwork cells

Myocilin (MYOC) was discovered more than 20 years ago and is the gene whose mutations are most commonly observed in individuals with glaucoma. Despite extensive research efforts, the function of WT MYOC has remained elusive, and how mutant MYOC is linked to glaucoma is unclear. Mutant MYOC is believed to be misfolded within the endoplasmic reticulum, and under normal physiological conditions misfolded MYOC should be retro-translocated to the cytoplasm for degradation. To better understand mutant MYOC pathology, we CRISPR-engineered a rat to have a MYOC Y435H substitution that is the equivalent of the pathological human MYOC Y437H mutation. Using this engineered animal model, we discovered that the chaperone αB-crystallin (CRYAB) is a MYOC-binding partner and that co-expression of these two proteins increases protein aggregates. Our results suggest that the misfolded mutant MYOC aggregates with cytoplasmic CRYAB and thereby compromises protein clearance mechanisms in trabecular meshwork cells, and this process represents the primary mode of mutant MYOC pathology. We propose a model by which mutant MYOC causes glaucoma, and we propose that therapeutic treatment of patients having a MYOC mutation may focus on disrupting the MYOC-CRYAB complexes.

Glaucoma Pred: Glaucoma prediction based on Myocilin genotype and phenotype information

Glaucoma is the second leading cause of blindness after cataract and is heterogeneous in nature. Employing a genetic approach for the detection of the diseased condition provides an advantage that the gene responsible for the disease can be identified by genetic test. The availability of predictive tests based on the published literature would provide a mechanism for early detection and treatment. The genotype and phenotype information could be a valuable source for predicting the risk of the disease. To this end, a web server has been developed, based on the genotype and phenotype of myocilin mutation, which were identified by familial linkage analysis and case studies. The proposed web server provides clinical data and severity index for a given mutation. The server has several useful options to help clinicians and researchers to identify individuals at a risk of developing the disease. Glaucoma Pred server is available at http://bioserver1.physics.iisc.ac.in/myocilin.

A novel single nucleotide polymorphism in exon 3 of MYOC enhances the risk of glaucoma

Genetic polymorphismsof MYOCalter the myocilin protein,which leads to disruption of thenormal regulation of intraocular pressure (IOP) that ultimately causes glaucoma.Theaim of the present study was to identify the polymorphism in exon 3 of the MYOC gene of theglaucoma patients in Lahore, Pakistan. We conducted a case-control study with 100 patients and 100 controls subjects. We extracted DNA from blood samples,amplified the target DNA fragmentby PCR, and identifiedpolymorphisms through sequencing. We observed that the allelic and genotypic frequencies of rs74315341 and rs879255525 were associated with glaucoma in our patient population. The polymorphism atrs74315341 led to the substitutionof serine for arginine,whereas the polymorphism at rs879255525 led to the substitution ofasparagine for lysine. The haplotype TGAAGCCATTTC was associated with disease onset, whereas the haplotype GGAAGCCATTTC was protective against disease development. In conclusion, weidentified MYOC gene polymorphisms in susceptible regions that were associated withglaucoma onset among the Lahore patient population.This is the first report to identify a novel mutation in rs879255525 in exon 3 of the MYOC genethat is associated withglaucoma.

Full-length myocilin protein is purified from mammalian cells as a dimer

Myocilin (MYOC) is a secreted protein found in human aqueous humor (AH) and mutations in the MYOC gene are the most common mutation observed in glaucoma patients. Human AH analyzed under non-reducing conditions suggests that MYOC is not normally found in a monomeric form, but rather is predominantly dimeric. Although MYOC was first reported almost 20 years ago, a technical challenge still faced by researchers is an inability to isolate full-length MYOC protein for experimental purposes. Herein we describe two methods by which to isolate sufficient quantities of human full-length MYOC protein from mammalian cells. One method involved identification of a cell line (HeLa S3) that would secrete full-length protein (15 mg/L) while the second method involved a purification approach from 293 cells requiring identification and modification of an internal MYOC cleavage site (Glu214/Leu215). MYOC protein yield from 293 cells was improved by mutation of two MYOC N-terminal cysteines (C47 and C61) to serines. Analytical size exclusion chromatography of our full-length MYOC protein purified from 293 cells indicated that it is predominantly dimeric and we propose a structure for the MYOC dimer. We hope that by providing methods to obtain MYOC protein, researchers will be able to utilize the protein to obtain new insights into MYOC biology. The ultimate goal of MYOC research is to better understand this target so we can help the patient that carries a MYOC mutation retain vision and maintain quality of life.

Are we ready for genetic testing for primary open-angle glaucoma?

Following a dramatic reduction in the cost of genotyping technology in recent years, there have been significant advances in the understanding of the genetic basis of glaucoma. Glaucoma patients represent around a quarter of all outpatient activity in the UK hospital eye service and are a huge burden for the National Health Service. A potential benefit of genetic testing is personalised glaucoma management, allowing direction of our limited healthcare resources to the glaucoma patients who most need it. Our review aims to summarise recent discoveries in the field of glaucoma genetics and to discuss their potential clinical utility. While genome-wide association studies have now identified over ten genes associated with primary open-angle glaucoma (POAG), individually, variants in these genes are not predictive of POAG in populations. There are data suggesting some of these POAG variants are associated with conversion from ocular hypertension to POAG and visual field progression among POAG patients. However, these studies have not been replicated yet and such genetic testing is not currently justified in clinical care. In contrast, genetic testing for inherited early-onset disease in relatives of POAG patients with a known genetic mutation is of clear benefit; this can support either regular review to commence early treatment when the disease develops, or discharge from ophthalmology services of relatives who do not carry the mutation. Genetic testing for POAG at a population level is not currently justified.

Genetics of glaucoma

Genetic and genomic studies, including genome-wide association studies (GWAS) have accelerated the discovery of genes contributing to glaucoma, the leading cause of irreversible blindness world-wide. Glaucoma can occur at all ages, with Mendelian inheritance typical for the rare early onset disease (before age 40) and complex inheritance evident in common adult-onset forms of disease. Recent studies have suggested possible therapeutic targets for some patients with early-onset glaucoma based on the molecular and cellular events caused by MYOC, OPTN and TBK1 mutations. Diagnostic genetic tests using early-onset glaucoma genes are also proving useful for pre-symptomatic disease detection and genetic counseling. Recent GWAS completed for three types of common adult-onset glaucoma have identified novel loci for POAG (primary-open-angle glaucoma) (ABCA1, AFAP1, GMDS, PMM2, TGFBR3, FNDC3B, ARHGEF12, GAS7, FOXC1, ATXN2, TXNRD2); PACG (primary angle-closure glaucoma (EPDR1, CHAT, GLIS3, FERMT2, DPM2-FAM102); and exfoliation syndrome (XFS) glaucoma (CACNA1A). In total sixteen genomic regions have been associated with POAG (including the normal tension glaucoma (NTG) subgroup), 8 with PACG and 2 with XFS. These studies are defining important biological pathways and processes that contribute to disease pathogenesis.

Phenotypic Description of the Spanish Multicentre Genetic Glaucoma Group Cohort

INTRODUCTION

The aim of the study was to make a phenotypic description of the Spanish multicentre glaucoma group cohort of patients.

DESIGN

Retrospective, observational, multicentre, cohort study.

MATERIAL AND METHODS

The clinical charts of 152 patients with hereditary glaucoma from18 Spanish eye centres were reviewed in order to make an epidemiologic description of the type of glaucoma and associated factors. True hereditary cases were compared with familiar cases according to the Gong et al. criteria.

RESULTS

61% were true hereditary cases and 39% familiar cases. Ocular comorbidity, optic disc damage, and visual field mean defect were significantly more severe in hereditary patients, who required significantly more first-line hypotensive drugs and surgical interventions to control intraocular pressure than familiar patients.

CONCLUSIONS

The strength of the hereditary component of glaucoma seems to worsen the clinical course, causing more structural and functional damage and requiring more intense glaucoma treatment. The family history of glaucoma should be carefully investigated and taken into consideration when making treatment decisions or intensifying previous treatment.

Major review: Molecular genetics of primary open-angle glaucoma

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

Glaucoma history and risk factors

Apart from the risk of developing glaucoma there is also the risk that it is not detected and irreversible loss of vision ensues. Some studies of methods of glaucoma diagnosis have examined the results of instrument-based examinations with great if not complete reliance on objective findings in arriving at a diagnosis. The very valuable advances in glaucoma detection instrument technologies, and apparent increasing dependence on them, may have led to reduced consideration of information available from a patient history in those studies. Dependence on objective evidence of glaucomatous pathology may reduce the possibility of detecting glaucoma suspects or patients at risk for becoming glaucoma suspects. A valid positive family history of glaucoma is very valuable information. However, negative family histories can often be unreliable due to large numbers of glaucoma cases being undiagnosed. No evidence of family history is appropriate rather than no family history. In addition the unreliability of a negative family history is increased when patients with glaucoma fail to inform their family members. A finding of no family history can only be stated as no known family history. In examining the potential diagnostic contribution from a patient history, this review considers, age, frailty, race, type and degree of refractive error, systemic hyper- and hypotension, vasospasm, migraine, pigmentary dispersion syndrome, pseudoexfoliation syndrome, obstructive sleep apnea syndrome, diabetes, medication interactions and side effects, the degree of exposure to intraocular and intracranial pressure elevations and fluctuations, smoking, and symptoms in addition to genetics and family history of the disease.

A novel de novo Myocilin variant in a patient with sporadic juvenile open angle glaucoma

Background

Glaucoma is a leading cause of irreversible blindness. Pathogenic variants in the Myocilin gene (MYOC) cause juvenile open angle glaucoma (JOAG) in 8–36 % of cases, and display an autosomal dominant inheritance with high penetrance. Molecular diagnosis is important for early identification as therapies are effective in minimizing vision loss and MYOC variants can be associated to severe glaucoma. MYOC variants are usually inherited, however a fifth of carriers do not report a family history. The occurrence of de novo MYOC variants is currently unknown.

Case presentation

In this study we investigated a 14 year old male Caucasian patient diagnosed with JOAG, and no family history of glaucoma. A novel probably deleterious MYOC:p.(Pro254Leu) variant was identified in the index case. This variant was not present in the parents or the siblings.

Conclusion

This is the second report of a de novo MYOC variant in a sporadic case of JOAG and it is currently unknown if this mechanism occurs more frequently. This finding emphasizes the importance of screening individuals with JOAG for MYOC mutations irrespective of a negative family history.

Clinical Characteristics of Juvenile-onset Open Angle Glaucoma

PURPOSE

To demonstrate the clinical characteristics of juvenile-onset open angle glaucoma (JOAG) and to evaluate the prognostic factors for visual field (VF) progression in eyes with JOAG.

METHODS

The medical records of 125 eyes of 72 patients with JOAG were analyzed retrospectively. At least four reliable VF tests were required to determine the VF progression, and the progression was defined using the modified Anderson criteria. Comparisons in clinical manifestations among groups were performed using independent t-test, and generalized estimating equations were also conducted.

RESULTS

The mean follow-up duration was 94.4 ± 50.5 months. Patients with JOAG showed a male preponderance (64 %), myopia (-4.99 ± 4.01 diopters) and a severe elevation of intraocular pressure (35.6 ± 10.8 mmHg). Forty-two JOAG patients (58 %) had complained of symptoms associated with vision and pain; however, one-third presented with no definite symptoms. Fifty-seven patients were diagnosed with JOAG in both eyes, and they were significantly older (p = 0.039) and had a greater family history (p = 0.035) than patients with unilateral JOAG. The progression group exhibited a significantly higher intraocular pressure at the last visit (p = 0.023) than the non-progression group.

CONCLUSIONS

Because patients with considerable JOAG had no definite symptoms, periodic eye examinations are needed. To prevent the VF's progression, JOAG patients may require more careful management of intraocular pressure.

Accurate Imputation-Based Screening of Gln368Ter Myocilin Variant in Primary Open-Angle Glaucoma

PURPOSE

Myocilin (MYOC) is a well-established primary open-angle glaucoma (POAG) risk gene, with rare variants known to have high penetrance. The most common clinically relevant risk variant, Gln368Ter, has an allele frequency of 0.1% to 0.3% in populations of European ancestry. Detection of rare MYOC variants has traditionally been conducted using Sanger sequencing. Here we report the use of genotyping arrays and imputation to assess whether rare variants including Gln368Ter can be reliably detected.

METHODS

A total of 1155 cases with advanced POAG and 1992 unscreened controls genotyped on common variant arrays participated in this study. Accuracy of imputation of Gln368Ter variants was compared with direct sequencing. A genome-wide association study was performed using additive model adjusted for sex and the first six principal components.

RESULTS

We found that although the arrays we used were designed to tag common variants, we could reliably impute the Gln368Ter variant (rs74315329). When tested in 1155 POAG cases and 1992 controls, rs74315329 was strongly associated with risk (odds ratio = 15.53, P = 1.07 × 10-9). All POAG samples underwent full sequencing of the MYOC gene, and we found a sensitivity of 100%, specificity of 99.91%, positive predictive value of 95.65%, and negative predictive value of 100% between imputation and sequencing. Gln368Ter was also accurately imputed in a further set of 1801 individuals without POAG. Among the total set of 3793 (1992 + 1801) individuals without POAG, six were predicted (probability > 95%) to carry the risk variant.

CONCLUSIONS

We demonstrate that some clinically important rare variants can be reliably detected using arrays and imputation. These results have important implications for the detection of clinically relevant incidental findings in ongoing and future studies using arrays.

Measurement of Systemic Mitochondrial Function in Advanced Primary Open-Angle Glaucoma and Leber Hereditary Optic Neuropathy

Primary Open Angle Glaucoma (POAG) is a common neurodegenerative disease characterized by the selective and gradual loss of retinal ganglion cells (RGCs). Aging and increased intraocular pressure (IOP) are glaucoma risk factors; nevertheless patients deteriorate at all levels of IOP, implying other causative factors. Recent evidence presents mitochondrial oxidative phosphorylation (OXPHOS) complex-I impairments in POAG. Leber Hereditary Optic Neuropathy (LHON) patients suffer specific and rapid loss of RGCs, predominantly in young adult males, due to complex-I mutations in the mitochondrial genome. This study directly compares the degree of OXPHOS impairment in POAG and LHON patients, testing the hypothesis that the milder clinical disease in POAG is due to a milder complex-I impairment. To assess overall mitochondrial capacity, cells can be forced to produce ATP primarily from mitochondrial OXPHOS by switching the media carbon source to galactose. Under these conditions POAG lymphoblasts grew 1.47 times slower than controls, whilst LHON lymphoblasts demonstrated a greater degree of growth impairment (2.35 times slower). Complex-I enzyme specific activity was reduced by 18% in POAG lymphoblasts and by 29% in LHON lymphoblasts. We also assessed complex-I ATP synthesis, which was 19% decreased in POAG patients and 17% decreased in LHON patients. This study demonstrates both POAG and LHON lymphoblasts have impaired complex-I, and in the majority of aspects the functional defects in POAG were milder than LHON, which could reflect the milder disease development of POAG. This new evidence places POAG in the spectrum of mitochondrial optic neuropathies and raises the possibility for new therapeutic targets aimed at improving mitochondrial function.

Genetics of Primary Inherited Disorders of the Optic Nerve: Clinical Applications

Inherited disorders of the optic nerve significantly impact vision in children and adults. The optic nerve disorders most commonly encountered clinically are glaucoma and primary optic neuropathy including Leber's hereditary optic neuropathy (LHON) and autosomal dominant or Kjer's optic atrophy. Current knowledge of the genetics of optic neuropathy and glaucoma makes it possible to test for mutations in disease-causing genes allowing for presymptomatic testing and risk assessment, and recent advances have revealed important disease mechanisms that may suggest potential therapeutic targets. In this perspective, we describe the current approaches and limitations to genetic testing for these disorders and provide an update on the development of gene-based therapies.

Developments in Ocular Genetics: 2013 Annual Review

PURPOSE

To highlight major advancements in ocular genetics from the year 2013.

DESIGN

Literature review.

METHODS

A literature search was conducted on PubMed to identify articles pertaining to genetic influences on human eye diseases. This review focuses on manuscripts published in print or online in the English language between January 1, 2013 and December 31, 2013. A total of 120 papers from 2013 were included in this review.

RESULTS

Significant progress has been made in our understanding of the genetic basis of a broad group of ocular disorders, including glaucoma, age-related macular degeneration, cataract, diabetic retinopathy, keratoconus, Fuchs' endothelial dystrophy, and refractive error.

CONCLUSIONS

The latest next-generation sequencing technologies have become extremely effective tools for identifying gene mutations associated with ocular disease. These technological advancements have also paved the way for utilization of genetic information in clinical practice, including disease diagnosis, prediction of treatment response and molecular interventions guided by gene-based knowledge.

Anticipation, anti-glaucoma drug treatment response and phenotype of a Chinese family with glaucoma caused by the Pro370Leu myocilin mutation

AIM

To describe the anticipation and anti-glaucoma drugs response of a Chinese family with juvenile-onset open angle glaucoma (JOAG) caused by the Pro370Leu myocilin (MYOC) mutation.

METHODS

Fifteen members of a three-generation Chinese family with JOAG were recruited to this study. They all underwent ophthalmic common examinations. Patients suspected to have JOAG got an assessment of visual field and optical coherence tomography. Intraocular pressures (IOPs) of four patients were measured at 8, 10, 12, 14, 17 o'clock respectively after using anti-glaucoma drugs. Mutation screening of all MYOC gene coding exons of the participants was performed by using direct sequencing of PCR products.

RESULTS

Clinical examinations and pedigree analysis revealed eight family members were suffered from JOAG. Apparent genetics anticipation phenomenon was observed in this family. Their clinical features included elevated IOP of 35-55mmHg, loss of visual field, thinning of retinal nerve fiber layer, and glaucomatous optic disc damage. Noticeably, their intraocular pressure levels could be controlled within normal range at 8 and 10 o'clock by anti-glaucoma drugs, but their IOPs would elevate >21mmHg after 12 o'clock. Seven patients received trabeculectomy produced thin-walled, pale, and saccate filtering blebs maintaining lower intraocular pressure efficiently. Mutation screening indentified a heterozygous C→T missense mutation in the MYOC gene at position 1 109 in exon 3, corresponding to a substitution of a highly conserved proline to leucine at codon 370 in the olfactomedin domain of MYOC.

CONCLUSION

The clinical characteristics of JOAG in this family were 1) genetics anticipation; 2) high IOP; 3) temporay response to anti-glaucoma drugs; 4) filtering surgery produced thin-walled and saccate filtering blebs, helping maintain lower IOP.