Copy number variations of TBK1 in Australian patients with primary open-angle glaucoma

Molecular genetics of inherited normal tension glaucoma

Normal tension glaucoma (NTG) is a complex optic neuropathy characterized by progressive retinal ganglion cell death and glaucomatous visual field loss, despite normal intraocular pressure (IOP). This condition poses a unique clinical challenge due to the absence of elevated IOP, a major risk factor in typical glaucoma. Recent research indicates that up to 21% of NTG patients have a family history of glaucoma, suggesting a genetic predisposition. In this comprehensive review using PubMed studies from January 1990 to December 2023, our focus delves into the genetic basis of autosomal dominant NTG, the only known form of inheritance for glaucoma. Specifically exploring optineurin ( OPTN ), TANK binding kinase 1 ( TBK1 ), methyltransferase-like 23 ( METTL23 ), and myocilin ( MYOC ) mutations, we summarize their clinical manifestations, mutant protein behaviors, relevant animal models, and potential therapeutic pathways. This exploration aims to illuminate the intricate pathogenesis of NTG, unraveling the contribution of these genetic components to its complex development.

Migraine headache and other risk factors associated with glaucoma among the adult population living in Armenia: a case-control study

PURPOSE

This study aimed to assess the association between migraine headache and glaucoma among the adult population living in Armenia.

METHODS

This case-control study recruited 145 cases with glaucoma and 250 controls without glaucoma and other ocular disorders except refractive error from Optomed Canada Diagnostic Eye Center in Armenia. A structured questionnaire contained questions on socio-demographics, family history of glaucoma and stroke, ocular health, smoking, migraine, and obstructive sleep apnea. The Migraine Screening Questionnaire assessed possible migraine and the Berlin Questionnaire measured obstructive sleep apnea.

RESULTS

The mean ages of cases and controls were 63.3 (SD = 12.3) and 39.5 (SD = 13.5), respectively. Females comprised 62.8% of cases and 69.1% of controls. A total of 17.8% of cases and 19.0% of controls had possible migraine. In the adjusted analysis older age (OR 1.17; 95% CI 1.12; 1.23), average/lower than average socio-economic status (OR 5.27; 95% CI 1.30; 21.3), and family history of glaucoma (OR 4.25; 95% CI 1.51; 11.9) were associated with high-tension glaucoma.

CONCLUSION

Timely case detection of glaucoma among those with average/low socio-economic status and those with family history of glaucoma could prevent further progression of the disease. Further studies to explore the relationship between migraine headache and specific types of glaucoma may be worthwhile.

Normal-Tension Glaucoma and Potential Clinical Links to Alzheimer's Disease

Glaucoma is a group of optic neuropathies and the world's leading cause of irreversible blindness. Normal-tension glaucoma (NTG) is a subtype of glaucoma that is characterized by a typical pattern of peripheral retinal loss, in which the patient's intraocular pressure (IOP) is considered within the normal range (<21 mmHg). Currently, the only targetable risk factor for glaucoma is lowering IOP, and patients with NTG continue to experience visual field loss after IOP-lowering treatments. This demonstrates the need for a better understanding of the pathogenesis of NTG and underlying mechanisms leading to neurodegeneration. Recent studies have found significant connections between NTG and cerebral manifestations, suggesting NTG as a neurodegenerative disease beyond the eye. Gaining a better understanding of NTG can potentially provide new Alzheimer's Disease diagnostics capabilities. This review identifies the epidemiology, current biomarkers, altered fluid dynamics, and cerebral and ocular manifestations to examine connections and discrepancies between the mechanisms of NTG and Alzheimer's Disease.

Glaucoma: from pathogenic mechanisms to retinal glial cell response to damage

Glaucoma is a neurodegenerative disease of the retina characterized by the irreversible loss of retinal ganglion cells (RGCs) leading to visual loss. Degeneration of RGCs and loss of their axons, as well as damage and remodeling of the lamina cribrosa are the main events in the pathogenesis of glaucoma. Different molecular pathways are involved in RGC death, which are triggered and exacerbated as a consequence of a number of risk factors such as elevated intraocular pressure (IOP), age, ocular biomechanics, or low ocular perfusion pressure. Increased IOP is one of the most important risk factors associated with this pathology and the only one for which treatment is currently available, nevertheless, on many cases the progression of the disease continues, despite IOP control. Thus, the IOP elevation is not the only trigger of glaucomatous damage, showing the evidence that other factors can induce RGCs death in this pathology, would be involved in the advance of glaucomatous neurodegeneration. The underlying mechanisms driving the neurodegenerative process in glaucoma include ischemia/hypoxia, mitochondrial dysfunction, oxidative stress and neuroinflammation. In glaucoma, like as other neurodegenerative disorders, the immune system is involved and immunoregulation is conducted mainly by glial cells, microglia, astrocytes, and Müller cells. The increase in IOP produces the activation of glial cells in the retinal tissue. Chronic activation of glial cells in glaucoma may provoke a proinflammatory state at the retinal level inducing blood retinal barrier disruption and RGCs death. The modulation of the immune response in glaucoma as well as the activation of glial cells constitute an interesting new approach in the treatment of glaucoma.

Familial normal tension glaucoma genetics

Glaucoma is defined by characteristic optic nerve damage and corresponding visual field defects and is the leading cause of irreversible blindness in the world. Elevated intraocular pressure (IOP) is a strong risk factor for developing glaucoma. However, glaucoma can occur at any IOP. Normal tension glaucoma (NTG) arises with IOPs that are within what has been defined as a normal range, i.e., 21 mm Hg or less, which may present challenges in its diagnosis and management. Identifying inheritance patterns and genetic mutations in families with NTG has helped elucidate mechanisms of NTG, however the pathophysiology is complex and not fully understood. Approximately 2% of NTG cases are caused primarily by mutations in single genes, optineurin (OPTN), TANK binding kinase 1 (TKB1), or myocilin (MYOC). Herein, we review pedigree studies of NTG and autosomal dominant NTG caused by OPTN, TBK1, and MYOC mutations. We review identified mutations and resulting clinical features of OPTN-associated and TBK1-associated NTG, including long-term follow up of these patients with NTG. In addition, we report a new four-generation pedigree of NTG caused by a Glu50Lys OPTN mutation, including six family members with a mean follow up of 17 years. Common features of OPTN -associated NTG due to Glu50Lys mutation included early onset of disease with an IOP <21 mm Hg, marked optic disc cupping, and progressive visual field loss which appeared to stabilize once an IOP of less than 10 mm Hg was achieved. Lastly, we review risk factor genes which have been identified to contribute to the complex inheritance of NTG.

Molecular genetics of primary open-angle glaucoma

Glaucoma is a series of linked optic diseases resulting in progressive vision loss and total blindness due to the acquired loss of retinal ganglion cells. This harm to the optic nerve results in visual impairment and, ultimately, total blindness if left untreated. Primary open-angle glaucoma (POAG) is the most frequent variety within the large family of glaucoma. It is a multifaceted and heterogeneous condition with several environmental and genetic variables aiding in its etiology. By 2040, there will be 111.8 million glaucoma patients globally, with Asia and Africa accounting for the vast majority. The goal of this review is to elaborate on the role of genes (nuclear and mitochondrial) as well as their variants in the pathogenesis of POAG. PubMed and Google Scholar databases were searched online for papers until September 2022. Prevalence and inheritance patterns vary significantly across different ethnic and geographic populations. Numerous causative genetic loci may exist; however, only a few have been recognized and characterized. Further investigation into the genetic etiology of POAG is expected to uncover novel and intriguing causal genes, allowing for a more precise pathogenesis pattern of the disease.

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

OBJECTIVES

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

METHODS

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

RESULTS

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

CONCLUSION

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

Regulatory mechanisms of retinal ganglion cell death in normal tension glaucoma and potential therapies

Normal tension glaucoma (NTG) is a multifactorial optic neuropathy characterized by normal intraocular pressure, progressive retinal ganglion cell (RGC) death, and glaucomatous visual field loss. Recent studies have described the mechanisms underlying the pathogenesis of NTG. In addition to controlling intraocular pressure, neuroprotection and reduction of RGC degeneration may be beneficial therapies for NTG. In this review, we summarized the main regulatory mechanisms of RGC death in NTG, including autophagy, glutamate neurotoxicity, oxidative stress, neuroinflammation, immunity, and vasoconstriction. Autophagy can be induced by retinal hypoxia and axonal damage. In this process, ischemia can cause mutations of optineurin and activate the nuclear factor-kappa B pathway. Glutamate neurotoxicity is induced by the over-stimulation of N-methyl-D-aspartate membrane receptors by glutamate, which occurs in RGCs and induces progressive glaucomatous optic neuropathy. Oxidative stress also participates in NTG-related glaucomatous optic neuropathy. It impairs the mitochondrial and DNA function of RGCs through the apoptosis signal-regulating kinase-JUN N-terminal kinase pathway. Moreover, it increases inflammation and the immune response of RGCs. Endothelin 1 causes endothelial dysfunction and impairment of ocular blood flow, promoting vasospasm and glaucomatous optic neuropathy, as a result of NTG. In conclusion, we discussed research progress on potential options for the protection of RGCs, including TANK binding kinase 1 inhibitors regulating autophagy, N-methyl-D-aspartate receptor antagonists inhibiting glutamate toxicity, ASK1 inhibitors regulating mitochondrial function, and antioxidants inhibiting oxidative stress. In NTG, RGC death is regulated by a network of mechanisms, while various potential targets protect RGCs. Collectively, these findings provide insight into the pathogenesis of NTG and potential therapeutic strategies.

Proteostasis in aging-associated ocular disease

Vision impairment has devastating consequences for the quality of human life. The cells and tissues associated with the visual process must function throughout one's life span and maintain homeostasis despite exposure to a variety of insults. Maintenance of the proteome is termed proteostasis, and is vital for normal cellular functions, especially at an advanced age. Here we describe basic aspects of proteostasis, from protein synthesis and folding to degradation, and discuss the current status of the field with a particular focus on major age-related eye diseases: age-related macular degeneration, cataract, and glaucoma. Our intent is to allow vision scientists to determine where and how to harness the proteostatic machinery for extending functional homeostasis in the aging retina, lens, and trabecular meshwork. Several common themes have emerged despite these tissues having vastly different metabolisms. Continued exposure to insults, including chronic stress with advancing age, increases proteostatic burden and reduces the fidelity of the degradation machineries including the ubiquitin-proteasome and the autophagy-lysosome systems that recognize and remove damaged proteins. This "double jeopardy" results in an exponential accumulation of cytotoxic proteins with advancing age. We conclude with a discussion of the challenges in maintaining an appropriate balance of protein synthesis and degradation pathways, and suggest that harnessing proteostatic capacities should provide new opportunities to design interventions for attenuating age-related eye diseases before they limit sight.

Functional and structural consequences of TBK1 missense variants in frontotemporal lobar degeneration and amyotrophic lateral sclerosis

Mutations in the Tank-binding kinase 1 (TBK1) gene were identified in 2015 in individuals with frontotemporal lobar degeneration (FTLD) and amyotrophic lateral sclerosis (ALS). They account for ∼3-4% of cases. To date, over 100 distinct mutations, including missense, nonsense, deletion, insertion, duplication, and splice-site mutations have been reported. While nonsense mutations are predicted to cause disease via haploinsufficiency, the mechanisms underlying disease pathogenesis with missense mutations is not fully elucidated. TBK1 is a kinase involved in neuroinflammation, which is commonly observed in these diseases. TBK1 also phosphorylates key autophagy mediators, thereby regulating proteostasis, a pathway that is dysregulated in ALS-FTLD. Recently, several groups have characterised various missense mutations with respect to their effects on the phosphorylation of known TBK1 substrates, TBK1 homodimerization, interaction with optineurin, and the regulation of autophagy and neuroinflammatory pathways. Further, the effects of either global or conditional heterozygous knock-out of Tbk1, or the heterozygous or homozygous knock-in of ALS-FTLD associated mutations, alone or when crossed with the SOD1^G93A classical ALS mouse model or a TDP-43 mouse model, have been reported. In this review we summarise the known functional effects of TBK1 missense mutations. We also present novel modelling data that predicts the structural effects of missense mutations and discuss how they correlate with the known functional effects of these mutations.

Prevalence of Open-angle Glaucoma in the Faroese Population

PURPOSE

The Faroe Islands are home to 50,000 genetically isolated people in the North Atlantic. The prevalence of open-angle glaucoma (OAG) in the Faroese population is unknown. Consequently, we conducted a survey to determine the prevalence of OAG in the Faroese population. We also investigated the role of known glaucoma-causing genes in Faroese OAG.

MATERIALS AND METHODS

We conducted a prospective survey of known and newly diagnosed glaucoma patients at the Faroese National Hospital, Landssjukrahusid, Tórshavn between October 1, 2015 to December 31, 2017. In addition we reviewed the only eye care provider in the Faroese Islands by scrutinizing electronic medical records between 2009 and June 15, 2014, October 1, 2015 and the partly overlapping prescriptions for ocular hypotensive medications in 2016 to identify patients with either a diagnosis of glaucoma, a diagnosis of ocular hypertension or a prescription for ocular hypotensive medications. Next, we prospectively confirmed diagnoses with complete eye examinations. Patient DNA samples were tested for variations in known glaucoma-causing genes [myocilin (MYOC), optineurin (OPTN), and TANK binding kinase 1 (TBK1)].

RESULTS

We determined the age-related prevalence of OAG January 1, 2017 in individuals 40 years or older to be 10.7/1000 (1.07%) and highly age-related. A diagnosis of OAG was present in 264 patients, of whom 211 (79.9%) had primary OAG (including normal tension glaucoma), 49 (18.6%) had pseudoexfoliation glaucoma, and 4 (1.5%) had pigmentary glaucoma. Among patients receiving medications for glaucoma, nearly 50% had primary OAG, while the majority of the rest had ocular hypertension or secondary glaucoma. No disease-causing variants were detected in MYOC, OPTN, or TBK1.

CONCLUSIONS

The calculated prevalence of OAG in the Faroe Islands was 1.07%. The absence of MYOC, OPTN, or TBK1 disease-causing variants in Faroese primary OAG patients suggests that a different, potentially unique set of genes may be contributing to the pathogenesis of glaucoma in this population.

Genetic association between CDKN2B-AS1 polymorphisms and the susceptibility of primary open-angle glaucoma (POAG): a meta-analysis from 21,775 subjects

Background

Primary open-angle glaucoma (POAG) is affected by both genetics and environmental factors. CDKN2B-AS1 polymorphisms have been reported to be involved in the pathogenesis of POAG. However, the results of the genetic associations between the CDKN2B-AS1 polymorphisms and POAG risk were inconclusive.

Aims

This study aimed to evaluate the correlation of CDKN2B-AS1 polymorphisms and POAG susceptibility using a meta-analysis.

Methods

Meta-analysis was performed by searching PubMed, Web of science, the Cochrane database of system reviews, CNKI, and Embase databases. The relationship of CDKN2B-AS1 rs4977756, rs10120688, rs2157719, and rs7049105 polymorphisms and POAG risk was evaluated by the odds ratios (ORs) and 95% confidence intervals (CIs).

Results

Eleven studies with 8290 cases and 13,485 controls were included in the present meta-analysis. The alleles of rs4977756 and rs10120688 significantly increased the risk of POAG (rs4977756: OR = 1.20, 95%CI = 1.03–1.39, p = 0.02; rs10120688: OR = 1.36, 95%CI = 1.29–1.44, p < 0.00001). As for ethnicity, rs4977756 polymorphism significantly increased POAG risk in Caucasians (OR = 1.33, 95%CI = 1.12–1.57, p = 0.0009), but not in Asians. In addition, the rs2157719 allele was significantly associated with POAG risk in Asians (OR = 0.66, 95%CI = 0.55–0.80, p < 0.0001), but not in Caucasians (p > 0.05).

Conclusions

The CDKN2B-AS1 rs4977756 might increase the POAG risk in Caucasian population, and rs2157719 might decrease the POAG risk in Asian population, while rs10120688 might increase the risk of POAG.

Genome-wide CNV investigation suggests a role for cadherin, Wnt, and p53 pathways in primary open-angle glaucoma

BACKGROUND

To investigate whether copy number variations (CNVs) are implicated in molecular mechanisms underlying primary open-angle glaucoma (POAG), we used genotype data of POAG individuals and healthy controls from two case-control studies, AGS (n = 278) and GLGS-UGLI (n = 1292). PennCNV, QuantiSNP, and cnvPartition programs were used to detect CNV. Stringent quality controls at both sample and marker levels were applied. The identified CNVs were intersected in CNV region (CNVR). After, we performed burden analysis, CNV-genome-wide association analysis, gene set overrepresentation and pathway analysis. In addition, in human eye tissues we assessed the expression of the genes lying within significant CNVRs.

RESULTS

We reported a statistically significant greater burden of CNVs in POAG cases compared to controls (p-value = 0,007). In common between the two cohorts, CNV-association analysis identified statistically significant CNVRs associated with POAG that span 11 genes (APC, BRCA2, COL3A1, HLA-DRB1, HLA-DRB5, HLA-DRB6, MFSD8, NIPBL, SCN1A, SDHB, and ZDHHC11). Functional annotation and pathway analysis suggested the involvement of cadherin, Wnt signalling, and p53 pathways.

CONCLUSIONS

Our data suggest that CNVs may have a role in the susceptibility of POAG and they can reveal more information on the mechanism behind this disease. Additional genetic and functional studies are warranted to ascertain the contribution of CNVs in POAG.

Development of Primary Open Angle Glaucoma-Like Features in a Rhesus Macaque Colony From Southern China

Purpose

To describe the ocular phenotype of spontaneous glaucoma in a non-human primate colony.

Methods

In total, 722 Rhesus macaque monkeys aged 10 to 25 years underwent optical coherence tomography (OCT), fundus photography (FP), and intraocular pressure (IOP) measurements. Monkeys with baseline cup-to-disc ratio (CDR) <0.5 were used to establish baseline ocular features. A subset was followed longitudinally for three years and compared to glaucoma suspects on the basis of OCT/FP criteria.

Results

The average IOP under ketamine sedation and average CDR for the entire colony was 13.0 ± 4.3 mm Hg and 0.38 ± 0.07, respectively. The mean baseline conscious IOP of glaucoma suspects (N = 18) versus controls (N = 108) was 16.2 ± 3.5 mm Hg and 13.9 ± 2.3 mm Hg, respectively (P = 0.001). All glaucoma suspects had unremarkable slit lamp examinations and open angles based on anterior segment OCT. Baseline global circumpapillary retinal nerve fiber layer (RNFL) thickness was 91.5 ± 11.0 µM versus 102.7 ± 8.5 µM in suspects and controls, respectively (P < 0.0001). All sectors on the baseline circumpapillary OCT showed a significant reduction in RNFL thickness versus controls (P ≤ 0.0022) except for the temporal sector (P ≥ 0.07). In three-year longitudinal analysis, neither CDR nor OCT parameters changed in controls (N = 40; P ≥ 0.16), whereas significant increase in CDR (P = 0.018) and nominally significant decreases in two OCT sectors (nasal, P = 0.023 and nasal inferior, P = 0.046) were noted in suspects.

Conclusions

Members of a nonhuman primate colony exhibit important ophthalmic features of human primary open-angle glaucoma.

Translational Relevance

Identification of a spontaneous model of glaucoma in nonhuman primates represents an unprecedented opportunity to elucidate the natural history, pathogenesis and effective therapeutic strategies for the disease.

Immunogenetics of the Ocular Anterior Segment: Lessons from Inherited Disorders

Autoimmune and autoinflammatory diseases cause morbidity in multiple organ systems including the ocular anterior segment. Genetic disorders of the innate and adaptive immune system present an avenue to study more common inflammatory disorders and host-pathogen interactions. Many of these Mendelian disorders have ophthalmic manifestations. In this review, we highlight the ophthalmic and molecular features of disorders of the innate immune system. A comprehensive literature review was performed using PubMed and the Online Mendelian Inheritance in Man databases spanning 1973-2020 with a focus on three specific categories of genetic disorders: RIG-I-like receptors and downstream signaling, inflammasomes, and RNA processing disorders. Tissue expression, clinical associations, and animal and functional studies were reviewed for each of these genes. These genes have broad roles in cellular physiology and may be implicated in more common conditions with interferon upregulation including systemic lupus erythematosus and type 1 diabetes. This review contributes to our understanding of rare inherited conditions with ocular involvement and has implications for further characterizing the effect of perturbations in integral molecular pathways.

Autophagy and ALS: mechanistic insights and therapeutic implications

Mechanisms of protein homeostasis are crucial for overseeing the clearance of misfolded and toxic proteins over the lifetime of an organism, thereby ensuring the health of neurons and other cells of the central nervous system. The highly conserved pathway of autophagy is particularly necessary for preventing and counteracting pathogenic insults that may lead to neurodegeneration. In line with this, mutations in genes that encode essential autophagy factors result in impaired autophagy and lead to neurodegenerative conditions such as amyotrophic lateral sclerosis (ALS). However, the mechanistic details underlying the neuroprotective role of autophagy, neuronal resistance to autophagy induction, and the neuron-specific effects of autophagy-impairing mutations remain incompletely defined. Further, the manner and extent to which non-cell autonomous effects of autophagy dysfunction contribute to ALS pathogenesis are not fully understood. Here, we review the current understanding of the interplay between autophagy and ALS pathogenesis by providing an overview of critical steps in the autophagy pathway, with special focus on pivotal factors impaired by ALS-causing mutations, their physiologic effects on autophagy in disease models, and the cell type-specific mechanisms regulating autophagy in non-neuronal cells which, when impaired, can contribute to neurodegeneration. This review thereby provides a framework not only to guide further investigations of neuronal autophagy but also to refine therapeutic strategies for ALS and related neurodegenerative diseases.Abbreviations: ALS: amyotrophic lateral sclerosis; Atg: autophagy-related; CHMP2B: charged multivesicular body protein 2B; DPR: dipeptide repeat; FTD: frontotemporal dementia; iPSC: induced pluripotent stem cell; LIR: LC3-interacting region; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MTOR: mechanistic target of rapamycin kinase; PINK1: PTEN induced kinase 1; RNP: ribonuclear protein; sALS: sporadic ALS; SPHK1: sphingosine kinase 1; TARDBP/TDP-43: TAR DNA binding protein; TBK1: TANK-binding kinase 1; TFEB: transcription factor EB; ULK: unc-51 like autophagy activating kinase; UPR: unfolded protein response; UPS: ubiquitin-proteasome system; VCP: valosin containing protein.

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.

The Role of Autophagy in Eye Diseases

Autophagy is a catabolic process that ensures homeostasis in the cells of our organism. It plays a crucial role in protecting eye cells against oxidative damage and external stress factors. Ocular pathologies of high incidence, such as age-related macular degeneration, cataracts, glaucoma, and diabetic retinopathy are of multifactorial origin and are associated with genetic, environmental factors, age, and oxidative stress, among others; the latter factor is one of the most influential in ocular diseases, directly affecting the processes of autophagy activity. Alteration of the normal functioning of autophagy processes can interrupt organelle turnover, leading to the accumulation of cellular debris and causing physiological dysfunction of the eye. The aim of this study is to review research on the role of autophagy processes in the main ocular pathologies, which have a high incidence and result in high costs for the health system. Considering the role of autophagy processes in cell homeostasis and cell viability, the control and modulation of autophagy processes in ocular pathologies could constitute a new therapeutic approach.

TBK1 interacts with tau and enhances neurodegeneration in tauopathy

One of the defining pathological features of Alzheimer's disease (AD) is the deposition of neurofibrillary tangles (NFTs) composed of hyperphosphorylated tau in the brain. Aberrant activation of kinases in AD has been suggested to enhance phosphorylation and toxicity of tau, making the responsible tau kinases attractive therapeutic targets. The full complement of tau-interacting kinases in AD brain and their activity in disease remains incompletely defined. Here, immunoaffinity enrichment coupled with mass spectrometry (MS) identified TANK-binding kinase 1 (TBK1) as a tau-interacting partner in human AD cortical brain tissues. We validated this interaction in human AD, familial frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17) caused by mutations in MAPT (R406W & P301L) and corticobasal degeneration (CBD) postmortem brain tissues as well as human cell lines. Further, we document increased TBK1 activation in both AD and FTDP-17 and map TBK1 phosphorylation sites on tau based on in vitro kinase assays coupled to MS. Lastly, in a Drosophila tauopathy model, activating expression of a conserved TBK1 ortholog triggers tau hyperphosphorylation and enhanced neurodegeneration, whereas knockdown had the reciprocal effect, suppressing tau toxicity. Collectively, our findings suggest that increased TBK1 activation may promote tau hyperphosphorylation and neuronal loss in AD and related tauopathies.

The role of TRPV4 channels in ocular function and pathologies

Transient potential receptor vanilloid 4 (TRPV4) is an ion channel responsible for sensing osmotic and mechanical signals, which in turn regulates calcium signaling across cell membranes. TRPV4 is widely expressed throughout the body, and plays an important role in normal physiological function, as well as different pathologies, however, its role in the eye is not well known. In the eye, TRPV4 is expressed in various tissues, such as the retina, corneal epithelium, ciliary body, and the lens. In this review, we provide an overview on TRPV4 structure, activation, mutations, and summarize the current knowledge of TRPV4 function and signaling mechanisms in various locations throughout the eye, as well as its role in ocular diseases, such as glaucoma and diabetic retinopathy. Based on the available data, we highlight the therapeutic potential of TRPV4 as well as the shortcomings of current research. Finally, we provide future perspectives on the implications of targeting TRPV4 to treat various ocular pathologies.

Genomic Characterization of TBK1 Duplication in Korean Normal-tension Glaucoma Patients

PRéCIS:: One (0.2%) of 418 Korean normal-tension glaucoma (NTG) patients had TBK1 duplication. The putative mechanism of TBK1 duplication in Korean NTG patients is the nonhomologous end-joining.

PURPOSE

TBK1 duplication is a genomic cause of familial NTG. NTG accounts for up to 90% of primary open-angle glaucoma in Koreans, with genetic tendency. We aimed to investigate the prevalence of TBK1 duplication in Korean NTG patients and to identify their genomic structure and duplication mechanism.

MATERIALS AND METHODS

We obtained DNA samples from 418 NTG patients and 195 healthy controls for evaluating TBK1 copy number variations using a semiquantitative polymerase chain reaction (PCR). The samples with TBK1 gene duplication were further confirmed using droplet digital PCR. The whole-genome sequencing of patient samples with duplications was performed to identify the accurate breakpoints and to elucidate the genomic structure. Ophthalmic evaluation and confirmation of TBK1 duplication using junction PCR were performed in families of positive patients.

RESULTS

TBK1 duplication was found in 1 of 418 NTG cases (0.2%). The duplication range was from g.64,803,151 to g.64,927,214 (124,063 bp). It is the smallest region of overlapping duplication in TBK1. Any repetitive sequences were not found near the breakpoints of our case. Inserted sequences were found within the breakpoints. A brother and a niece of the positive case appeared the typical clinical features of NTG and shared the same TBK1 duplications with the index case.

CONCLUSIONS

In Korea, the prevalence of TBK1 duplication was 0.2% and the smallest reported TBK1 duplication associated with NTG was found. The mechanism of TBK1 duplication was suggested to be nonhomologous end-joining while a previous report pointed out the mechanism of TBK1 duplications as nonallelic homologous recombination.

Genetic Variants Associated With the Onset and Progression of Primary Open-Angle Glaucoma

PURPOSE

We sought to investigate the genetic variants associated with the onset and progression of primary open-angle glaucoma (POAG).

DESIGN

Case-control genetic association study.

METHODS

Japanese POAG patients (n = 505) and control subjects (n = 246) were genotyped for 22 genetic variants predisposing to POAG that can be classified into those associated with intraocular pressure (IOP) elevation (IOP-related genetic variants) and optic nerve vulnerability independent of IOP (non-IOP-related genetic variants). The total number of risk alleles of the 17 IOP-related and 5 non-IOP-related genetic variants were calculated as the genetic risk score (GRS), and the associations between the GRS and family history of glaucoma as an indicator of POAG onset and age at the diagnosis of glaucoma as an indicator of POAG progression were evaluated.

RESULTS

There was a significant association (P = .014; odds ratio 1.26 per GRS) between the non-IOP-related GRS, but not IOP-related GRS, and a family history of glaucoma in POAG. As the non-IOP-related GRS increased, the risk of a family history of glaucoma increased. In contrast, a significant association (P = .0014; β = -0.14) was found between the IOP-related GRS, but not non-IOP-related GRS, and age at the diagnosis of glaucoma. As the IOP-related GRS increased, age at the diagnosis of glaucoma decreased.

CONCLUSION

The results indicate that non-IOP-related (optic nerve vulnerability) rather than IOP-related (IOP elevation) genetic variants may play an important role in the onset of POAG (family history of glaucoma) and that IOP-related rather than non-IOP-related genetic variants may play an important role in its progression (age at the diagnosis of glaucoma).

Genetics of primary open-angle glaucoma and its endophenotypes

Glaucoma is a neurodegenerative disorder characterized by the loss of retinal ganglion cells and optic nerve fibers, resulting in the loss of visual field. Primary open-angle glaucoma (POAG) is the most prevalent subtype of glaucoma. Recent genome-wide association studies (GWASs) identified more than 100 variants associated with POAG and multiple loci associated with endophenotypes including the disc area, vertical cup-to-disc ratio (VCDR), and intraocular pressure (IOP). Especially, several GWASs reported the association between VCDR and variants near CDKN2B/CDKN2B-AS1, ATOH7, and CHEK2, and between IOP and variants near TMCO1, CAV1/CAV2, GAS7, and ARHGEF12. However, the effect of each variant on endophenotypes is modest; therefore, it is useful to construct a genetic risk score (GRS) based on the effect on endophenotypes by combining susceptible genetic variants. Several studies demonstrated that higher GRS was closely associated with endophenotypes including the VCDR, IOP, and age of diagnosis. Henceforth, by quantifying GRS, identification of high risk group before the disease onset, prediction of visual prognosis and early intervention may be possible.

The Genetic and Endoplasmic Reticulum-Mediated Molecular Mechanisms of Primary Open-Angle Glaucoma

Glaucoma is a heterogenous, chronic, progressive group of eye diseases, which results in irreversible loss of vision. There are several types of glaucoma, whereas the primary open-angle glaucoma (POAG) constitutes the most common type of glaucoma, accounting for three-quarters of all glaucoma cases. The pathological mechanisms leading to POAG pathogenesis are multifactorial and still poorly understood, but it is commonly known that significantly elevated intraocular pressure (IOP) plays a crucial role in POAG pathogenesis. Besides, genetic predisposition and aggregation of abrogated proteins within the endoplasmic reticulum (ER) lumen and subsequent activation of the protein kinase RNA-like endoplasmic reticulum kinase (PERK)-dependent unfolded protein response (UPR) signaling pathway may also constitute important factors for POAG pathogenesis at the molecular level. Glaucoma is commonly known as a ‘silent thief of sight’, as it remains asymptomatic until later stages, and thus its diagnosis is frequently delayed. Thereby, detailed knowledge about the glaucoma pathophysiology is necessary to develop both biochemical and genetic tests to improve its early diagnosis as well as develop a novel, ground-breaking treatment strategy, as currently used medical therapies against glaucoma are limited and may evoke numerous adverse side-effects in patients.

Long-Term Follow-Up of Normal Tension Glaucoma Patients With TBK1 Gene Mutations in One Large Pedigree

PURPOSE

To characterize features of glaucoma associated with a TANK binding kinase 1 (TBK1) gene duplication, which is among the most common molecularly defined causes of normal tension glaucoma (NTG).

DESIGN

Retrospective observational case series.

METHODS

We conducted a retrospective case series, by reviewing medical records of 7 members of a pedigree with NTG caused by TBK1 gene duplications. Clinical features of these patients at diagnosis, throughout management, and at latest follow-up were identified, including age, intraocular pressure (IOP), central corneal thickness (CCT), optic nerve head appearance, and mean deviation (MD) assessed with Humphrey visual field (HVF) testing protocols.

RESULTS

At initial diagnosis, the mean age was 35 ± 7 years, IOP was 16 ± 2.1 mm Hg, cup-to-disc (C/D) ratio was 0.9 ± 0.08, and MD assessed via HVF 30-2 and/or 24-2 testing protocols was -9.0 ± 8.9 (range: -1.8 to -27) dB in the 14 study eyes. At initial diagnosis, 4 of 14 eyes (28%) had no visual field defect, 4 (28%) had early visual field defects, and 6 (43%) had severe visual field defects. Patients had a mean follow-up of 21.5 ± 9.0 years and experienced an average reduction of IOP by 28%. Four of 12 eyes (33%) had stable visual fields throughout follow-up, while 8 eyes (67%) had slow-to-moderate progression. The 30-2 and/or 24-2 HVF tests had an average change in MD of -0.53 ± 0.26 dB/year. No eyes had rapid progression with an MD >1.0 dB/year. At final follow-up, the mean IOP was 11.5 ± 2.9, and C/D ratio was 0.94 ± 0.4. At final follow-up, 3 of 14 eyes (21%) had early visual field defects, 4 (29%) had moderate visual field defects, and 7 (50%) had severe visual field defects. Six of 14 eyes (43%) met criteria for legal blindness.

CONCLUSIONS

We provide the first report of the clinical features and long-term clinical course in a family of NTG patients with TBK1 gene duplications. TBK1-associated glaucoma exhibits classic features of NTG. Patients present with severe disease at a relatively early age and most (67%) have slow-to-moderate progression of their visual field defects. The rate of visual field change appears correlated with the magnitude of IOP, suggesting that it may be advantageous to set extremely low IOP targets for some patients with TBK1-associated glaucoma.

Association of Ambient Particulate Matter Exposure with the Incidence of Glaucoma in Childhood

PURPOSE

We investigated whether exposure to air pollution, particularly to particles with a mass median aerodynamic diameter of ≤10 μm (PM₁₀), is associated with diagnosis of childhood glaucoma.

DESIGN

Retrospective cohort study.

METHODS

From the National Health Insurance Service-National Sample Cohort, a total of 9004 infants born between January 2002 and December 2002 were included and followed-up for an 11-year period (2003-2012). Patients with glaucoma were defined as International Classification of Diseases, 10th revision code H40. Exposure levels of PM₁₀ were extrapolated using geographic information systems, and individual exposure levels were assigned.

RESULTS

During the study period, glaucoma occurred in 85 patients (0.94%). The probability of developing childhood glaucoma increased with the increase in PM₁₀ quartiles. Increases in 1 μg/m³ of long-term PM₁₀ were significantly associated with increased hazard ratios (HRs) for childhood glaucoma (HR = 1.22 [95% confidence interval {CI} 1.15-1.28]). Compared with risk of the lowest PM₁₀ exposure group (quartile 1), the adjusted HRs for childhood glaucoma were significant in the highest PM₁₀ exposure group of quartile 4 (HR = 2.84 [95% CI 1.37-5.89]) in model 3. Regarding the long-term PM₁₀ exposure, the estimated hazard was considerably elevated in quartile 4 (HR = 6.61 [95% CI 2.96-14.75]).

CONCLUSIONS

Short-term and long-term exposure to PM₁₀ was associated with the incidence of childhood glaucoma. This finding confirms previous reports on the link between air pollution and ocular disease and suggests that PM₁₀ exposure may be a risk for childhood glaucoma.

An Intraocular Pressure Polygenic Risk Score Stratifies Multiple Primary Open-Angle Glaucoma Parameters Including Treatment Intensity

PURPOSE

To examine the combined effects of common genetic variants associated with intraocular pressure (IOP) on primary open-angle glaucoma (POAG) phenotype using a polygenic risk score (PRS) stratification.

DESIGN

Cross-sectional study.

PARTICIPANTS

For the primary analysis, we examined the glaucoma phenotype of 2154 POAG patients enrolled in the Australian and New Zealand Registry of Advanced Glaucoma, including patients recruited from the United Kingdom. For replication, we examined an independent cohort of 624 early POAG patients.

METHODS

Using IOP genome-wide association study summary statistics, we developed a PRS derived solely from IOP-associated variants and stratified POAG patients into 3 risk tiers. The lowest and highest quintiles of the score were set as the low- and high-risk groups, respectively, and the other quintiles were set as the intermediate risk group.

MAIN OUTCOME MEASURES

Clinical glaucoma phenotype including maximum recorded IOP, age at diagnosis, number of family members affected by glaucoma, cup-to-disc ratio, visual field mean deviation, and treatment intensity.

RESULTS

A dose-response relationship was found between the IOP PRS and the maximum recorded IOP, with the high genetic risk group having a higher maximum IOP by 1.7 mmHg (standard deviation [SD], 0.62 mmHg) than the low genetic risk group (P = 0.006). Compared with the low genetic risk group, the high genetic risk group had a younger age of diagnosis by 3.7 years (SD, 1.0 years; P < 0.001), more family members affected by 0.46 members (SD, 0.11 members; P < 0.001), and higher rates of incisional surgery (odds ratio, 1.5; 95% confidence interval, 1.1-2.0; P = 0.007). No statistically significant difference was found in mean deviation. We further replicated the maximum IOP, number of family members affected by glaucoma, and treatment intensity (number of medications) results in the early POAG cohort (P ≤ 0.01).

CONCLUSIONS

The IOP PRS was correlated positively with maximum IOP, disease severity, need for surgery, and number of affected family members. Genes acting via IOP-mediated pathways, when considered in aggregate, have clinically important and reproducible implications for glaucoma patients and their close family members.

Autophagy and Age-Related Eye Diseases

Background

Autophagy is a catabolic process that depends on the lysosome. It is usually used to maintain cellular homeostasis, survival and development by degrading abnormal substances and dysfunctional organelles, especially when the cell is exposed to starvation or other stresses. Increasing studies have reported that autophagy is associated with various eye diseases, of which aging is one of the important factors.

Objective

To summarize the functional and regulatory role of autophagy in ocular diseases with aging, and discuss the possibility of autophagy-targeted therapy in age-related diseases.

Methods

PubMed searches were performed to identify relevant articles published mostly in the last 5 years. The key words were used to retrieve including “autophagy”, “aging”, “oxidative stress AND autophagy”, “dry eye AND autophagy”, “corneal disease AND autophagy”, “glaucoma AND autophagy”, “cataract AND autophagy”, “AMD AND autophagy”, “cardiovascular diseases AND autophagy”, “diabetes AND autophagy”. After being classified and assessed, the most relevant full texts in English were chosen.

Results

Apart from review articles, more than two research articles for each age-related eye diseases related to autophagy were retrieved. We only included the most relevant and recent studies for summary and discussion.

Conclusion

Autophagy has both protective and detrimental effects on the progress of age-related eye diseases. Different types of studies based on certain situations in vitro showed distinct results, which do not necessarily coincide with the actual situation in human bodies completely. It means the exact role and regulatory function of autophagy in ocular diseases remains largely unknown. Although autophagy as a potential therapeutic target has been proposed, many problems still need to be solved before it applies to clinical practice.

Effects of ALS-associated TANK binding kinase 1 mutations on protein-protein interactions and kinase activity

Exonic DNA sequence variants in the Tbk1 gene associate with both sporadic and familial amyotrophic lateral sclerosis (ALS). Here, we examine functional defects in 25 missense TBK1 mutations, focusing on kinase activity and protein-protein interactions. We identified kinase domain (KD) mutations that abolish kinase activity or display substrate-specific defects in specific pathways, such as innate immunity and autophagy. By contrast, mutations in the scaffold dimerization domain (SDD) of TBK1 can cause the loss of kinase activity due to structural disruption, despite an intact KD. Familial ALS mutations in ubiquitin-like domain (ULD) or SDD display defects in dimerization; however, a subset retains kinase activity. These observations indicate that TBK1 dimerization is not required for kinase activation. Rather, dimerization seems to increase protein stability and enables efficient kinase-substrate interactions. Our study revealed many aspects of TBK1 activities affected by ALS mutations, highlighting the complexity of disease pathogenicity and providing insights into TBK1 activation mechanism.

Association of LOXL1 Gene Polymorphisms with Exfoliation Glaucoma Patients

BACKGROUND

Pseudoexfoliation syndrome (XFS) is pathogenetically related to exfoliative glaucoma (XFG), which is the most common type of secondary glaucoma. We aimed to investigate the relationship between LOXL1 SNPs (rs1048661, rs3825942) and XFS and/or XFG in a cohort of Iranian subjects.

METHODS

This cross-sectional study investigated possible association between LOXL1 gene polymorphisms and exfoliative glaucoma in Northeastern part of Iran between May 2014 and May 2015. Sixty unrelated XFS/XFG patients, as well as 40 control subjects, were studied by direct sequencing. In fifteen senile cataract patients without glaucoma and fifteen patients with coexisting XFG and cataract, capsulorhexis specimen of the anterior lens capsule was used to evaluate LOXL1 gene transcripts by Real-Time PCR technique. We analyzed the results for allele frequencies and haplotype association and investigated the relative gene expression.

RESULTS

Significant associations between the rs382594 SNP and XFG and between rs1048661 SNP and XFG were observed (P<0.05 for both). The frequency of the G allele in the exonic SNP (rs1048661) appeared to be higher in XFS or XFG patients compared to control subjects (P= 0.0497). Moreover, in the rs3825942 SNP, the G allele was more frequent in XFS/XFG patients compared to control subjects (P=0.0016). The highest cumulative frequency was for the GG haplotype. GG haplotype was associated with increased risk of XFG compared to the rs1048661 G/T and rs3825942 G/A haplotypes. LOXL1 mRNA expression was not statistically significantly different between XFS/XFG and control subjects.

CONCLUSION

We reported the LOXL1 gene polymorphism in an Iranian XFS/XFG cohort. Similar to many other ethnic groups and geographic regions, our results confirmed an association between LOXL1 gene variants and XFG in Iran.

Association of TNF-α gene alterations (c.-238G>A, c.-308G>A, c.-857C>T, c.-863C>A) with primary glaucoma in north Indian cohort

BACKGROUND

Tumor Necrosis Factor-alpha (TNF-α) a pleuripotent pro-inflammatory cytokine, is involved in retinal ganglion cells apoptosis in glaucoma. Thus present study aimed to analyze the association of TNF-α promoter region alterations (c.-238G>A (rs361525), c.-308G>A (rs1800629), c.-857C>T (rs1799724) and c.-863C>A (rs1800630)) with glaucoma in north Indian cohort.

METHODS

Present hospital based case control study involved 286 glaucoma patients (Primary Open Angle Glaucoma [POAG], Primary Angle Closure Glaucoma [PACG], Primary Congenital Glaucoma [PCG]) and 300 controls. TNF-α gene alteration (c.-238G>A (also referred as c.-418G>A; NM_000594.3)), c.-308G>A (c.-488G>A; NM_000594.3), c.-857C>T (c.-1037C>T; NM_000594.3) and c.-863C>A (c.-1043C>A; NM_000594.3) harboring regions were PCR amplified and sequenced by Sanger sequencing. Allele frequency and genotype distribution in glaucoma cases and controls were compared using chi-square test and genetic association tested using different genetic models.

RESULTS

Statistically significant genotype and allelic association was observed between glaucoma cases and controls for c.-308G>A and c.-863C>A alterations (p = 0.001, p = 0.001; p = 0.001, p = 0.001 respectively). AA genotype of c.-308G>A conferred ~7 fold increased risk towards glaucoma (OR = 6.82, 95% CI = 2.82-16.53, p = 0.001). c.-863C>A alteration under dominant, recessive and co-dominant genetic models conferred ~2 fold increased risk for glaucoma. However, no association for c.-238G>A and c.-857C>T variants with glaucoma was observed. Further, three haplotypes (GGCA, GACC and GACA) (OR = 0.48, 95% CI = 0.35-0.67, p = 0.001; OR = 0.58, 95% CI = 0.36-0.91, p = 0.019 and OR = 0.16, 95% CI = 0.05-0.51, p = 0.002, respectively) conferred protective role towards glaucoma.

CONCLUSIONS

Present study is the first to indicate significant association of c.-308G>A and c.-863C>A alterations with glaucoma in cases from north Indian cohort. Also it is the first study from India to analyze the association and interaction of four promoter region alterations (c.-238G>A, c.-308G>A, c.-857C>T and c.-863C>A) in TNF-α resulting in three protective haplotypes.

Neuroinflammation in frontotemporal dementia

Frontotemporal dementia (FTD) refers to a group of progressive neurodegenerative disorders with different pathological signatures, genetic variability and complex disease mechanisms, for which no effective treatments exist. Despite advances in understanding the underlying pathology of FTD, sensitive and specific fluid biomarkers for this disease are lacking. As in other types of dementia, mounting evidence suggests that neuroinflammation is involved in the progression of FTD, including cortical inflammation, microglial activation, astrogliosis and differential expression of inflammation-related proteins in the periphery. Furthermore, an overlap between FTD and autoimmune disease has been identified. The most substantial evidence, however, comes from genetic studies, and several FTD-related genes are also implicated in neuroinflammation. This Review discusses specific evidence of neuroinflammatory mechanisms in FTD and describes how advances in our understanding of these mechanisms, in FTD as well as in other neurodegenerative diseases, might facilitate the development and implementation of diagnostic tools and disease-modifying treatments for FTD.

Mendelian genes in primary open angle glaucoma

Mutations in each of three genes, myocilin (MYOC), optineurin (OPTN), and TANK binding kinase 1 (TBK1), may cause primary open-angle glaucoma (POAG) that is inherited as a Mendelian trait. MYOC mutations cause 3-4% of POAG cases with IOP >21 mmHg, while mutations in OPTN, TBK1, and MYOC each cause ∼1% of POAG with IOP ≤21 mmHg, i.e. normal tension glaucoma. Identification of these disease-causing genes has provided insights into glaucoma pathogenesis. Mutations in MYOC cause a cascade of abnormalities in the trabecular meshwork including intracellular retention of MYOC protein, decreased aqueous outflow, higher intraocular pressure, and glaucoma. Investigation of MYOC mutations demonstrated that abnormal retention of intracellular MYOC and stimulation of endoplasmic reticular (ER) stress may be important steps in the development of MYOC-associated glaucoma. Mutations in OPTN and TBK1 cause a dysregulation of autophagy which may directly cause retinal ganglion cell damage and normal tension glaucoma. Discovery of these Mendelian causes of glaucoma has also provided a new set of potential therapeutic targets that may ultimately lead to novel, gene-directed glaucoma treatments.

Retinoic acid worsens ATG10-dependent autophagy impairment in TBK1-mutant hiPSC-derived motoneurons through SQSTM1/p62 accumulation

Mutations in the TBK1 (TANK binding kinase 1) gene are causally linked to amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). TBK1 phosphorylates the cargo receptors OPTN and SQSTM1 regulating a critical step in macroautophagy/autophagy. Disruption of the autophagic flux leads to accumulation of cytosolic protein aggregates, which are a hallmark of ALS. hiPSC-derived TBK1-mutant motoneurons (MNs) showed reduced TBK1 levels and accumulation of cytosolic SQSTM1-positive aggresomes. By screening a library of nuclear-receptor-agonists for modifiers of the SQSTM1 aggregates, we identified 4-hydroxy(phenyl)retinamide (4HPR) as a potent modifier exerting detrimental effects on mutant-TBK1 motoneurons fitness exacerbating the autophagy overload. We have shown by TEM that TBK1-mutant motoneurons accumulate immature phagophores due a failure in the elongation phase, and 4HPR further worsens the burden of dysfunctional phagophores. 4HPR-increased toxicity was associated with the upregulation of SQSTM1 in a context of strongly reduced ATG10, while rescue of ATG10 levels abolished 4HPR toxicity. Finally, we showed that 4HPR leads to a downregulation of ATG10 and to an accumulation of SQSTM1⁺ aggresomes also in hiPSC-derived C9orf72-mutant motoneurons. Our data show that cultured human motoneurons harboring mutations in TBK1 gene display typical ALS features, like decreased viability and accumulation of cytosolic SQSTM1-positive aggresomes. The retinoid 4HPR appears a strong negative modifier of the fitness of TBK1 and C9orf72-mutant MNs, through a pathway converging on the mismatch of initiated autophagy and ATG10 levels. Thus, autophagy induction appears not to be a therapeutic strategy for ALS unless the specific underlying pathway alterations are properly addressed. Abbreviations: 4HPR: 4-hydroxy(phenyl)retinamide; AKT: AKT1 serine/threonine kinase 1; ALS: amyotrophic lateral sclerosis; ATG: autophagy related; AVs: autophagic vesicle; C9orf72: chromosome 9 open reading frame 72; CASP3: caspase 3; CHAT: choline O-acetyltransferase; CYCS: cytochrome c, somatic; DIV: day in vitro; FTD: frontotemporal dementia; FUS: FUS RNA binding protein; GFP: green fluorescent protein; hiPSCs: human induced pluripotent stem cells; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MNs: motoneurons; mRFP: monomeric red fluorescent protein; MTOR: mechanistic target of rapamycin kinase; NFE2L2/NRF2: nuclear factor, erythroid 2 like 2; RARA: retinoic acid receptor alpha; SLC18A3/VACHT: solute carrier family 18 (vesicular acetylcholine transporter), member 3; SQSTM1/p62: sequestosome 1; TBK1: TANK binding kinase 1; TEM: transmission electron microscopy.

Role of Optineurin in the Mitochondrial Dysfunction: Potential Implications in Neurodegenerative Diseases and Cancer

Optineurin (Optn) is a 577 aa protein encoded by the Optn gene. Mutations of Optn are associated with normal tension glaucoma and amyotrophic lateral sclerosis, and its gene has also been linked to the development of Paget’s disease of bone and Crohn’s disease. Optn is involved in diverse cellular functions, including NF-κB regulation, membrane trafficking, exocytosis, vesicle transport, reorganization of actin and microtubules, cell cycle control, and autophagy. Besides its role in xenophagy and autophagy of aggregates, Optn has been identified as a primary autophagy receptor, among the five adaptors that translocate to mitochondria during mitophagy. Mitophagy is a selective macroautophagy process during which irreparable mitochondria are degraded, preventing accumulation of defective mitochondria and limiting the release of reactive oxygen species and proapoptotic factors. Mitochondrial quality control via mitophagy is central to the health of cells. One of the important surveillance pathways of mitochondrial health is the recently defined signal transduction pathway involving the mitochondrial PTEN-induced putative kinase 1 (PINK1) protein and the cytosolic RING-between-RING ubiquitin ligase Parkin. Both of these proteins, when mutated, have been identified in certain forms of Parkinson’s disease. By targeting ubiquitinated mitochondria to autophagosomes through its association with autophagy related proteins, Optn is responsible for a critical step in mitophagy. This review reports recent discoveries on the role of Optn in mitophagy and provides insight into its link with neurodegenerative diseases. We will also discuss the involvement of Optn in other pathologies in which mitophagy dysfunctions are involved including cancer.

Normal tension glaucoma: review of current understanding and mechanisms of the pathogenesis

Normal tension glaucoma (NTG) is an exception in the "glaucoma family" where the major risk factor, increased intraocular pressure, is missing. If not increased intraocular pressure, then what other causes can then lead to glaucomatous optic disc change and visual field loss in NTG? Several possibilities will be discussed. Among them a higher sensitivity to normal pressure, vascular dysregulation, an abnormally high translaminar pressure gradient and a neurodegenerative process due to impaired cerebrospinal fluid dynamics in the optic nerve sheath compartment. There are many excellent review papers published on normal tension glaucoma (NTG). The aim of this paper is therefore not to add another extensive review on NTG but rather to focus on and to discuss some possible mechanisms that are thought to be involved in the pathophysiology of NTG and to discuss the stronger and weaker aspects of each concept. The fact that several concepts exist suggests that NTG is still not very well understood and that no single mechanism on its own might adequately explain NTG.

Genomic Organization of TBK1 Copy Number Variations in Glaucoma Patients

BACKGROUND

Approximately 1% of normal tension glaucoma (NTG) cases are caused by TANK-binding kinase 1 (TBK1) gene duplications and triplications. However, the precise borders and orientation of these TBK1 gene copy number variations (CNVs) on chromosome 12 are unknown.

METHODS

We determined the exact borders of TBK1 CNVs and the orientation of duplicated or triplicated DNA segments in 5 NTG patients with different TBK1 mutations using whole-genome sequencing.

RESULTS

Tandemly duplicated chromosome segments spanning the TBK1 gene were detected in 4 NTG patients, each with unique borders. Four of 5 CNVs had borders located within interspersed repetitive DNA sequences (Alu and long interspersed nuclear element-L1 elements), suggesting that mismatched homologous recombinations likely generated these CNVs. A fifth NTG patient had a complex rearrangement including triplication of a chromosome segment spanning the TBK1 gene.

CONCLUSIONS

No specific mutation hotspots for TBK1 CNVs were detected, however, interspersed repetitive sequences (ie, Alu elements) were identified at the borders of TBK1 CNVs, which suggest that mismatch of these elements during meiosis may be the mechanism that generated TBK1 gene dosage mutations.

The Relation Between Endothelial Nitric Oxide Synthase Polymorphisms and Normal Tension Glaucoma

PURPOSE

We investigated whether polymorphisms of the endothelial NO synthase (eNOS) gene are associated with normal tension glaucoma (NTG). We also investigated whether the eNOS polymorphisms are associated with NTG subgroups [NTG with and without optic disc hemorrhage (DH)].

METHODS

A total of 251 patients with NTG and 245 healthy volunteers were enrolled in this study. DNA from peripheral blood leukocytes was extracted, and the genotypes of 4 polymorphisms (rs2070744, rs1549758, rs1799983, and rs2566514) in the eNOS gene were determined using restriction fragment length polymorphism and the SNaPshot method. The primary outcome was to investigate the relation between eNOS polymorphisms and NTG. The secondary outcome was to compare the frequencies of the polymorphic genotypes among the NTG subgroups. Bonferroni correction was used to adjust for type I error.

RESULTS

In all subjects, the genotype distribution was in accordance with Hardy-Weinberg equilibrium. None of the 4 polymorphisms showed any significant difference in the frequencies of alleles or genotypes between the NTG patients and controls. In the further analysis comparing the genotypic frequencies between NTG with DH and normal controls, the CC/CT genotype of rs2070744 was significantly associated with DH in NTG patients (genotypic association test, P-value=0.0041). On the multiple logistic regression analysis adjusted for covariates such as sex and age, the NTG with DH was associated with polymorphic genotypes of rs2070744 with a borderline significance (additive genetic model, P=0.0070).

CONCLUSIONS

Our results indicates that eNOS rs2070744 can be associated with NTG patients with DH. This finding suggests that the eNOS polymorphism may be a genetic risk factor in the development of DH in NTG patients.

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.

Genetics and genetic testing for glaucoma

PURPOSE OF REVIEW

In recent decades, investigators have identified numerous genes and genetic factors that cause or contribute risk for glaucoma. These findings have increased our understanding of disease mechanisms, provided us with new diagnostic tools, and may allow for development of improved therapies for glaucoma. However, genetic testing is most useful when it is reserved for appropriate patients. The purpose of this article is to review key points and recent developments regarding the genetics and genetic testing for glaucoma and to provide recommendations for when genetic testing may be warranted.

RECENT FINDINGS

Large genome-wide association studies have identified multiple new susceptibility loci associated with primary open angle glaucoma and primary angle closure glaucoma.

SUMMARY

Several glaucoma-causing genes and genetic risk factors for glaucoma have been discovered. As a result, there are specific clinical scenarios in which genetic testing is warranted. In select cases (i.e., familial juvenile open angle glaucoma), genetic testing can serve as a powerful tool to improve diagnostic accuracy, efficiency of disease surveillance, and selection of treatment, enabling physicians to better optimize care for their patients.

Partial duplication of the CRYBB1-CRYBA4 locus is associated with autosomal dominant congenital cataract

Congenital cataract is a rare but severe paediatric visual impediment, often caused by variants in one of several crystallin genes that produce the bulk of structural proteins in the lens. Here we describe a pedigree with autosomal dominant isolated congenital cataract and linkage to the crystallin gene cluster on chromosome 22. No rare single nucleotide variants or short indels were identified by exome sequencing, yet copy number variant analysis revealed a duplication spanning both CRYBB1 and CRYBA4. While the CRYBA4 duplication was complete, the CRYBB1 duplication was not, with the duplicated CRYBB1 product predicted to create a gain of function allele. This association suggests a new genetic mechanism for the development of isolated congenital cataract.

Whole exome sequencing implicates eye development, the unfolded protein response and plasma membrane homeostasis in primary open-angle glaucoma

PURPOSE

To identify biological processes associated with POAG and its subtypes, high-tension (HTG) and normal-tension glaucoma (NTG), by analyzing rare potentially damaging genetic variants.

METHODS

A total of 122 and 65 unrelated HTG and NTG participants, respectively, with early onset advanced POAG, 103 non-glaucoma controls and 993 unscreened ethnicity-matched controls were included in this study. Study participants without myocilin disease-causing variants and non-glaucoma controls were subjected to whole exome sequencing on an Illumina HiSeq2000. Exomes of participants were sequenced on an Illumina HiSeq2000. Qualifying variants were rare in the general population (MAF < 0.001) and potentially functionally damaging (nonsense, frameshift, splice or predicted pathogenic using SIFT or Polyphen2 software). Genes showing enrichment of qualifying variants in cases were selected for pathway and network analysis using InnateDB.

RESULTS

POAG cases showed enrichment of rare variants in camera-type eye development genes (p = 1.40×10-7, corrected p = 3.28×10-4). Implicated eye development genes were related to neuronal or retinal development. HTG cases were significantly enriched for key regulators in the unfolded protein response (UPR) (p = 7.72×10-5, corrected p = 0.013). The UPR is known to be involved in myocilin-related glaucoma; our results suggest the UPR has a role in non-myocilin causes of HTG. NTG cases showed enrichment in ion channel transport processes (p = 1.05×10-4, corrected p = 0.027) including calcium, chloride and phospholipid transporters involved in plasma membrane homeostasis. Network analysis also revealed enrichment of the MHC Class I antigen presentation pathway in HTG, and the EGFR1 and cell-cycle pathways in both HTG and NTG.

CONCLUSION

This study suggests that mutations in eye development genes are enriched in POAG. HTG can result from aberrant responses to protein misfolding which may be amenable to molecular chaperone therapy. NTG is associated with impaired plasma membrane homeostasis increasing susceptibility to apoptosis.

TBK1: a new player in ALS linking autophagy and neuroinflammation

Amyotrophic lateral sclerosis (ALS) is an adult-onset neurodegenerative disorder affecting motor neurons, resulting in progressive muscle weakness and death by respiratory failure. Protein and RNA aggregates are a hallmark of ALS pathology and are thought to contribute to ALS by impairing axonal transport. Mutations in several genes known to contribute to ALS result in deposition of their protein products as aggregates; these include TARDBP, C9ORF72, and SOD1. In motor neurons, this can disrupt transport of mitochondria to areas of metabolic need, resulting in damage to cells and can elicit a neuroinflammatory response leading to further neuronal damage. Recently, eight independent human genetics studies have uncovered a link between TANK-binding kinase 1 (TBK1) mutations and ALS. TBK1 belongs to the IKK-kinase family of kinases that are involved in innate immunity signaling pathways; specifically, TBK1 is an inducer of type-1 interferons. TBK1 also has a major role in autophagy and mitophagy, chiefly the phosphorylation of autophagy adaptors. Several other ALS genes are also involved in autophagy, including p62 and OPTN. TBK1 is required for efficient cargo recruitment in autophagy; mutations in TBK1 may result in impaired autophagy and contribute to the accumulation of protein aggregates and ALS pathology. In this review, we focus on the role of TBK1 in autophagy and the contributions of this process to the pathophysiology of ALS.

Transgenic TBK1 mice have features of normal tension glaucoma

Duplication of the TBK1 gene is associated with 1-2% of normal tension glaucoma, a common cause of vision loss and blindness that occurs without grossly abnormal intraocular pressure. We generated a transgenic mouse that has one copy of the human TBK1 gene (native promoter and gene structure) incorporated into the mouse genome (Tg-TBK1). Expression of the TBK1 transgene in the retinae of these mice was demonstrated by real-time PCR. Using immunohistochemistry TBK1 protein was predominantly localized to the ganglion cell layer of the retina, the cell type most affected by glaucoma. More intense TBK1 labelling was detected in the retinal ganglion cells (RGCs) of Tg-TBK1 mice than in wild-type littermates. Tg-TBK1 mice exhibit the cardinal sign of glaucoma, a progressive loss of RGCs. Hemizygous Tg-TBK1 mice (with one TBK1 transgene per genome) had a 13% loss of RGCs by 18 months of age (P = 1.5 × 10-8). Homozygous Tg-TBK1 mice had 7.6% fewer RGCs than hemizygous Tg-TBK1 mice and 20% fewer RGCs than wild-type mice (P = 1.9 × 10-5) at 6 months of age. No difference in intraocular pressures was detected between Tg-TBK1 mice and wild-type littermates as they aged (P > 0.05). Tg-TBK1 mice with extra doses of the TBK1 gene recapitulate the phenotype of normal tension glaucoma in human patients with a TBK1 gene duplication. Together, these studies confirm the pathogenicity of the TBK1 gene duplication in human glaucoma and suggest that excess production of TBK1 kinase may have a role in the pathology of glaucoma.

Tank-Binding Kinase 1 (TBK1) Gene and Open-Angle Glaucomas (An American Ophthalmological Society Thesis)

PURPOSE

To investigate the role of TANK-binding kinase 1 (TBK1) gene copy-number variations (ie, gene duplications and triplications) in the pathophysiology of various open-angle glaucomas.

METHODS

In previous studies, we discovered that copy-number variations in the TBK1 gene are associated with normal-tension glaucoma. Here, we investigated the prevalence of copy-number variations in cohorts of patients with other open-angle glaucomas-juvenile-onset open-angle glaucoma (n=30), pigmentary glaucoma (n=209), exfoliation glaucoma (n=225), and steroid-induced glaucoma (n=79)-using a quantitative polymerase chain reaction assay.

RESULTS

No TBK1 gene copy-number variations were detected in patients with juvenile-onset open-angle glaucoma, pigmentary glaucoma, or steroid-induced glaucoma. A TBK1 gene duplication was detected in one (0.44%) of the 225 exfoliation glaucoma patients.

CONCLUSIONS

TBK1 gene copy-number variations (gene duplications and triplications) have been previously associated with normal-tension glaucoma. An exploration of other open-angle glaucomas detected a TBK1 copy-number variation in a patient with exfoliation glaucoma, which is the first example of a TBK1 mutation in a glaucoma patient with a diagnosis other than normal-tension glaucoma. A broader phenotypic range may be associated with TBK1 copy-number variations, although mutations in this gene are most often detected in patients with normal-tension glaucoma.

Intraocular pressure and glaucoma: Is physical exercise beneficial or a risk?

Intraocular pressure may become elevated with muscle exertion, changes in body position and increased respiratory volumes, especially when Valsalva manoeuver mechanisms are involved. All of these factors may be present during physical exercise, especially if hydration levels are increased. This review examines the evidence for intraocular pressure changes during and after physical exercise. Intraocular pressure elevation may result in a reduction in ocular perfusion pressure with the associated possibility of mechanical and/or ischaemic damage to the optic nerve head. A key consideration is the possibility that, rather than being beneficial for patients who are susceptible to glaucomatous pathology, any intraocular pressure elevation could be detrimental. Lower intraocular pressure after exercise may result from its elevation causing accelerated aqueous outflow during exercise. Also examined is the possibility that people who have lower frailty are more likely to exercise as well as less likely to have or develop glaucoma. Consequently, lower prevalence of glaucoma would be expected among people who exercise. The evidence base for this topic is deficient and would be greatly improved by the availability of tonometry assessment during dynamic exercise, more studies which control for hydration levels, and methods for assessing the potential general health benefits of exercise against any possibility of exacerbated glaucomatous pathology for individual patients who are susceptible to such changes.