Genetic, Biochemical and Clinical Insights into Primary Congenital Glaucoma

Increasing the diagnostic yield of childhood glaucoma cases recruited into the 100,000 Genomes Project

Childhood glaucoma (CG) encompasses a heterogeneous group of genetic eye disorders that is responsible for approximately 5% of childhood blindness worldwide. Understanding the molecular aetiology is key to improving diagnosis, prognosis and unlocking the potential for optimising clinical management. In this study, we investigated 86 CG cases from 78 unrelated families of diverse ethnic backgrounds, recruited into the Genomics England 100,000 Genomes Project (GE100KGP) rare disease cohort, to improve the genetic diagnostic yield. Using the Genomics England/Genomic Medicine Centres (GE/GMC) diagnostic pipeline, 13 unrelated families were solved (13/78, 17%). Further interrogation using an expanded gene panel yielded a molecular diagnosis in 7 more unrelated families (7/78, 9%). This analysis effectively raises the total number of solved CG families in the GE100KGP to 26% (20/78 families). Twenty-five percent (5/20) of the solved families had primary congenital glaucoma (PCG), while 75% (15/20) had secondary CG; 53% of this group had non-acquired ocular anomalies (including iris hypoplasia, megalocornea, ectopia pupillae, retinal dystrophy, and refractive errors) and 47% had non-acquired systemic diseases such as cardiac abnormalities, hearing impairment, and developmental delay. CYP1B1 was the most frequently implicated gene, accounting for 55% (11/20) of the solved families. We identified two novel likely pathogenic variants in the TEK gene, in addition to one novel pathogenic copy number variant (CNV) in FOXC1. Variants that passed undetected in the GE100KGP diagnostic pipeline were likely due to limitations of the tiering process, the use of smaller gene panels during analysis, and the prioritisation of coding SNVs and indels over larger structural variants, CNVs, and non-coding variants.

Prevalence of Glu323Lys Mutation of the TIGR/MYOC Gene and Risk Factors amongst Primary Open-angle Glaucoma Patients in Ouagadougou, Burkina Faso

Aim

Glaucoma is a group of degenerative diseases of the optic nerve whose predisposing factors may be genetic. The objective of this study was to estimate the frequency of the Glu323Lys mutation as a genetic risk factor for glaucoma.

Materials and methods

A cross-sectional study over 6 months from October 2020 to March 2021 in Ouagadougou, Burkina Faso. A total of 89 samples of patients with primary open-angle glaucoma (POAG) were collected. The frequency of the Glu323Lys mutation of the myocilin, trabecular meshwork inducible glucocorticoid response (TIGR/MYOC) gene by polymerase chain reaction (PCR)-restriction fragment length polymorphism.

Results

In glaucoma patients, only homozygous nonmutated guanine-guanine (GG) and heterozygous mutated adenine-guanine (AG) genotypes were found in 96.63 and 3.37% of cases, respectively. Around 69.66% of patients had a family history of glaucoma, 28.09% had a history of hypertension, and 7.86% had a history of diabetes.

Conclusion

The frequency of the Glu323Lys mutation of the TIGR/MYOC gene was 3.37% in the glaucoma population in Ouagadougou. A case-control study is necessary to know the contribution of the Glu323Lys mutation as a genetic risk factor for glaucoma in our study population.

Clinical significance

This study constituted the beginning of genetic investigations of glaucoma in our context and showed a low Glu323Lys mutation.

How to cite this article

Traoré L, Sanou J, Bakyono BS, et al. Prevalence of Glu323Lys Mutation of the TIGR/MYOC Gene and Risk Factors amongst Primary Open-angle Glaucoma Patients in Ouagadougou, Burkina Faso. J Curr Glaucoma Pract 2023;17(2):79-84.

Screening of high-risk deleterious missense variations in the CYP1B1 gene implicated in the pathogenesis of primary congenital glaucoma: A comprehensive in silico approach

Background

Primary congenital glaucoma (PCG) is the most common subtype of glaucoma caused by defects in the cytochrome P450 1B1 (CYP1B1) gene. It is developing among infants in more than 80% of cases who exhibit impairments in the anterior chamber angle and the trabecular meshwork. Thus, a comprehensive in silico approach was performed to evaluate the effect of high-risk deleterious missense variations in the CYP1B1 gene.

Material and methods

All the information for CYP1B1 missense variants was retrieved from the dbSNP database. Seven different tools, namely: SIFT, PolyPhen-2, PROVEAN, SNAP2, PANTHER, PhD-SNP, and Predict-SNP, were used for functional annotation, and two packages, which were I-Mutant 2.0 and MUpro, were used to predict the effect of the variants on protein stability. A phylogenetic conservation analysis using deleterious variants was performed by the ConSurf server. The 3D structures of the wild-type and mutants were generated using the I-TASSER tool, and a 50 ns molecular dynamic simulation (MDS) was executed using the GROMACS webserver to determine the stability of mutants compared to the native protein. Co-expression, protein-protein interaction (PPI), gene ontology (GO), and pathway analyses were additionally performed for the CYP1B1 in-depth study.

Results

All the retrieved data from the dbSNP database was subjected to functional, structural, and phylogenetic analysis. From the conducted analyses, a total of 19 high-risk variants (P52L, G61E, G90R, P118L, E173K, D291G, Y349D, G365W, G365R, R368H, R368C, D374N, N423Y, D430E, P442A, R444Q, F445L, R469W, and C470Y) were screened out that were considered to be deleterious to the CYP1B1 gene. The phylogenetic analysis revealed that the majority of the variants occurred in highly conserved regions. The MD simulation analysis exhibited that all mutants' average root mean square deviation (RMSD) values were higher compared to the wild-type protein, which could potentially cause CYP1B1 protein dysfunction, leading to the severity of the disease. Moreover, it has been discovered that CYP1A1, VCAN, HSD17B1, HSD17B2, and AKR1C3 are highly co-expressed and interact with CYP1B1. Besides, the CYP1B1 protein is primarily involved in the metabolism of xenobiotics, chemical carcinogenesis, the retinal metabolic process, and steroid hormone biosynthesis pathways, demonstrating its multifaceted and important roles.

Discussion

This is the first comprehensive study that adds essential information to the ongoing efforts to understand the crucial role of genetic signatures in the development of PCG and will be useful for more targeted gene-disease association studies.

Novel compound heterozygous mutations in CYP1B1 identified in a Chinese family with developmental glaucoma

Developmental glaucoma, a subset of glaucoma, is associated with trabeculodysgenesis and/or anterior segment dysgenesis. It is one of the major causes of childhood blindness. Understanding its genetic background is important to diagnose, and identify potential therapeutic targets, of this disease. The present study aimed to detect the molecular origin of developmental glaucoma in a Chinese pedigree and its association with glaucomatous phenotypes. A three‑generation pedigree with developmental glaucoma was analyzed in the current study; a thorough ocular examination was performed on the proband and other individuals in the family. Genomic DNA was extracted from the peripheral blood of each individual, and possible disease‑causing genes were screened for mutations using a candidate gene panel. Exons and adjacent regions of the target genes were captured and enriched by probe hybridization. The enriched genes were sequenced on an Illumina high‑throughput sequencer. Variations were verified in other family members using Sanger sequencing. Disease causing mutations were analyzed by comparing the sequences and the structures of wild‑type and mutated cytochrome P450 family 1 subfamily B member 1 (CYP1B1) proteins using PyMOL software. The proband was diagnosed with developmental glaucoma and his parents and other relatives were asymptomatic. Novel compound heterozygous mutations, c.3G>A (p.M1I) and c.1310C>T (p.P437L), in CYP1B1 were detected in the proband, with the former inherited from his father and the latter from his mother. The c.3G>A (p.M1I) change is a novel mutation that disrupts the ATG start codon in exon one of CYP1B1 and therefore interferes with the translation start site. In conclusion, the findings of the present study suggested that the aforementioned compound heterozygous mutations in CYP1B1 may have caused developmental glaucoma in this Chinese family. The c.3G>A mutation in CYP1B1 is a novel mutation, and this study expands the gene mutation spectrum of CYP1B1.

Epidemiology and clinical presentation of glaucoma in a referral facility in Ghana: Any lessons for public health intervention?

The purpose of this study was to evaluate the epidemiological and clinical profile of patients living with glaucoma and receiving care in a tertiary eye center in Ghana. This was a hospital-based retrospective study of clinical records of glaucoma patients from January 2010 to December 2019. The study involved collating demographic information of patients, clinical presentation, and the management of glaucoma. A total of nineteen thousand (19,000) charts were retrieved from the eye center's archives. Out of these, 660 (3.5%) records of patients qualified for the study and were analyzed. There were 398 (60.3%) males and 262 (39.7%) females. Their ages ranged from 9 to 86 years (mean age = 47.30; SD ± 16.86 years). The averages of ocular parameters of 1,320 eyes (660 patients) were visual acuity = 0.26 ± 0.55 logMAR; intraocular pressure: 17.31 ± 6.11 mmHg; cup-to-disc ratios: 0.67 ± 0.17 D; and the average retinal nerve fibers thickness was 95.03 ± 21.74 μm. The mainstay of treatment was the sole use of medication. Males were the major group receiving glaucoma care at the tertiary level. Glaucoma cases included juveniles but the mean age suggests most were of adult-onset. Socio-demographic characteristics affected the diagnosis and management of glaucoma among patients receiving care at a referral center. Public health, stakeholders, and policymakers' interventions can help identify individuals with glaucoma.

Maternal diet as a risk factor for primary congenital glaucoma and defects of the anterior segment of the eye in the National Birth Defects Prevention Study

Primary congenital glaucoma (PCG) and anterior segment defects (ASDs) are rare ocular malformations diagnosed early in life which can cause blindness. Pathogenic variants in several genes have been linked to these conditions, but little is known about nongenetic risk factors. We investigated the association between maternal nutrition and PCG and ASDs in the National Birth Defects Prevention Study, a large population-based, multicenter case-control study of major birth defects in the United States. Mothers of cases (n = 152) and control infants without a birth defect (n = 9,178) completed an interview which included a food frequency questionnaire capturing usual dietary intake in the year before pregnancy. Maternal nutrition was assessed through individual nutrient intake, calculating a Diet Quality Index for Pregnancy (DQI-P) score for each mother, and using latent class analysis to empirically derive four dietary patterns. We calculated adjusted odds ratios (aORs) and 95% confidence intervals (CI) using logistic regression. The results for individual nutrients varied, with some having an inverse or U-shaped pattern of association with increasing intake. The DQI-P was not associated with risk of PCG and ASDs (aOR 0.91; CI 0.49-1.66, highest vs. lowest quartile). The dietary pattern analysis suggested lower odds among women with a Prudent and Mexican dietary pattern (aOR 0.82, 95% CI 0.52-1.29; aOR 0.80, 95% CI 0.36-1.78, respectively) compared to those with a Western dietary pattern. We found that higher intake of some nutrients and certain dietary patterns may be inversely associated with PCG and ASDs, though caution is urged due to imprecision of estimates.

Primary congenital glaucoma: An updated review

Primary congenital glaucoma (PCG) is a rare disease affecting children early in life. PCG was considered untreatable with inevitable blindness. However, recent advances in biochemical and genetic studies, the introduction of new diagnostic tools, intraocular pressure (IOP) lowering medications and improvement of surgical techniques have led to a better understanding of this devastating disease and preserving the vision of affected children. This paper presents an updated and broad overview of PCG in terms of the epidemiology and genetic aspects, particularly in Saudi Arabia, the clinical presentation and diagnostic approach to PCG with major emphasis on the treatment options.

Cholinergic nervous system and glaucoma: From basic science to clinical applications

The cholinergic system has a crucial role to play in visual function. Although cholinergic drugs have been a focus of attention as glaucoma medications for reducing eye pressure, little is known about the potential modality for neuronal survival and/or enhancement in visual impairments. Citicoline, a naturally occurring compound and FDA approved dietary supplement, is a nootropic agent that is recently demonstrated to be effective in ameliorating ischemic stroke, traumatic brain injury, Parkinson's disease, Alzheimer's disease, cerebrovascular diseases, memory disorders and attention-deficit/hyperactivity disorder in both humans and animal models. The mechanisms of its action appear to be multifarious including (i) preservation of cardiolipin, sphingomyelin, and arachidonic acid contents of phosphatidylcholine and phosphatidylethanolamine, (ii) restoration of phosphatidylcholine, (iii) stimulation of glutathione synthesis, (iv) lowering glutamate concentrations and preventing glutamate excitotoxicity, (v) rescuing mitochondrial function thereby preventing oxidative damage and onset of neuronal apoptosis, (vi) synthesis of myelin leading to improvement in neuronal membrane integrity, (vii) improving acetylcholine synthesis and thereby reducing the effects of mental stress and (viii) preventing endothelial dysfunction. Such effects have vouched for citicoline as a neuroprotective, neurorestorative and neuroregenerative agent. Retinal ganglion cells are neurons with long myelinated axons which provide a strong rationale for citicoline use in visual pathway disorders. Since glaucoma is a form of neurodegeneration involving retinal ganglion cells, citicoline may help ameliorate glaucomatous damages in multiple facets. Additionally, trans-synaptic degeneration has been identified in humans and experimental models of glaucoma suggesting the cholinergic system as a new brain target for glaucoma management and therapy.

Compound heterozygous mutations in CYP1B1 gene leads to severe primary congenital glaucoma phenotype

AIM

To identify the novel mutation alleles in the CYP1B1 gene of primary congenital glaucoma (PCG) patients at Shandong Province of China, and investigate their correlation with glaucomatous features.

METHODS

The DNA from the peripheral blood of 13 congenital glaucoma patients and 50 ethnically matched healthy controls from the affiliated hospital of Qingdao University were extracted. The coding region of the CYP1B1 gene was amplified by PCR and direct DNA sequencing was performed. Disease causing-variants were analyzed by comparing the sequences and the structures of wild type and mutant CYP1B1 proteins by PyMOL software.

RESULTS

Two missense mutations, including A330F caused by c.988G>T&c.989C>T, and R390H caused by c.1169G>A, were identified in one of the 13 PCG patients analyzed in our study. A330F mutation was observed to be novel in the Chinese Han population, which dramatically altered the protein structure of CYP1B1 gene, including the changes in the ligand-binding pocket. Furthermore, R390H mutation caused the changes in heme-protein binding site of this gene. In addition, the clinical phenotype displayed by PCG patient with these mutations was more pronounced than other PCG patients without these mutations. Multiple surgeries and combined drug treatment were not effective in reducing the elevated intraocular pressure in this patient.

CONCLUSION

A novel A330F mutation is identified in the CYP1B1 gene of Chinese PCG patient. Moreover, in combination with other mutation R390H, this PCG patient shows significant difference in the CYP1B1 protein structure, which may specifically contribute to severe glaucomatous phenotype.

Primary congenital glaucoma including next-generation sequencing-based approaches: clinical utility gene card

1. NAME OF THE DISEASE (SYNONYMS): Primary congenital glaucoma (PCG). Glaucoma, congenital (GLC). 2. OMIM# OF THE DISEASE: 231300- GLC3A. 600975- GLC3B. 613085- GLC3C. 613086- GLC3D. 617272- GLC3E. 3. NAME OF THE ANALYSED GENES OR DNA/CHROMOSOME SEGMENTS: CYP1B1. LTBP2. MYOC. FOXC1. TEK. 4. OMIM# OF THE GENE(S): CYP1B1 MIM# 601771. LTBP2 MIM# 602091. MYOC MIM# 601652. FOXC1 MIM# 601090. TEK MIM# 600221. Review of the analytical and clinical validity, as well as of the clinical utility of DNA-based testing for variants in the CYP1B1, LTBP2 and MYOC gene(s) in ⊠ diagnostic, ⊠ predictive and ⊠ prenatal settings and for ⊠ risk assessment in relatives.

Research progress on human genes involved in the pathogenesis of glaucoma (Review)

Glaucoma is the leading cause of irreversible blindness globally. It is known that the incidence of glaucoma is closely associated with inheritance. A large number of studies have suggested that genetic factors are involved in the occurrence and development of glaucoma, and even affect the drug sensitivity and prognosis of glaucoma. In the present review, 22 loci of glaucoma are presented, including the relevant genes (myocilin, interleukin 20 receptor subunit B, optineurin, ankyrin repeat- and SOCS box-containing protein 10, WD repeat-containing protein 36, EGF-containing fibulin-like extracellular matrix protein 1, neurotrophin 4, TANK-binding kinase 1, cytochrome P450 subfamily I polypeptide 1, latent transforming growth factor β binding protein 2 and TEK tyrosine kinase endothelial) and 74 other genes (including toll-like receptor 4, sine oculis homeobox Drosophila homolog of 1, doublecortin-like kinase 1, RE repeats-encoding gene, retinitis pigmentosa GTPase regulator-interacting protein, lysyl oxidase-like protein 1, heat-shock 70-kDa protein 1A, baculoviral IAP repeat-containing protein 6, 5,10-methylenetetrahydrofolate reductase and nitric oxide synthase 3 and nanophthalmos 1) that are more closely associated with glaucoma. The pathogenesis of these glaucoma-associated genes, glaucomatous genetics and genetic approaches, as well as glaucomatous risk factors, including increasing age, glaucoma family history, high myopia, diabetes, ocular trauma, smoking, intraocular pressure increase and/or fluctuation were also discussed.

A review on ocular findings in mouse lemurs: potential links to age and genetic background

Mouse lemurs, the world's smallest primates, inhabit forests in Madagascar. They are nocturnal, arboreal and dependent on vision for their everyday lives. In the last decades, the grey mouse lemur became increasingly important for biomedical research, in particular aging research. Experiments which require the combination of visual fitness and old age consequently depend on a solid knowledge of ocular pathologies. Although ocular diseases in mouse lemurs have been described as being common, they have not received much attention so far. Yet it is important to know when and why ocular diseases in captive mouse lemurs may occur. This review aims to provide a comprehensive overview of known ocular findings in mouse lemurs. It summarizes the frequency of ocular findings in captive mouse lemur colonies and points to their likely causes and treatment options based on the evidence available from other animals and humans. In addition, it shall be discussed whether age or genetic background may affect their development. This review may be used as a reference for future studies which require an assessment of visual performance in mouse lemurs and help to evaluate observed clinical signs and ocular diseases. Furthermore, the high incidence of specific diseases may provide new perspectives and set the groundwork for a new animal model for ocular research.

CYP1B1-mediated Pathobiology of Primary Congenital Glaucoma

CYP1B1 is a dioxin-inducible enzyme belonging to the cytochrome P450 superfamily. It has been observed to be important in a variety of developmental processes including in utero development of ocular structures. Owing to its role in the developmental biology of eye, its dysfunction can lead to ocular developmental defects. This has been found to be true and CYP1B1 mutations have been observed in a majority of primary congenital glaucoma (PCG) patients from all over the globe. Primary congenital glaucoma is an irreversibly blinding childhood disorder (onset at birth or early infancy) typified by anomalous development of trabecular meshwork (TM). How CYP1B1 causes PCG is not known; however, some basic investigations have been reported. Understanding the CYP1B1 mediated etiopathomechanism of PCG is very important to identify targets for therapy and preventive management. In this perspective, we will make an effort to reconstruct the pathomechanism of PCG in the light of already reported information about the disease and the CYP1B1 gene.

How to cite this article: Faiq MA, Dada R, Qadri R, Dada T. CYP1 B1-mediated Pathobiology of Primary Congenital Glaucoma. J Curr Glaucoma Pract 2015;9(3):77-80.

A novel methodology for enhanced and consistent heterologous expression of unmodified human cytochrome P450 1B1 (CYP1B1)

Cytochrome P450 1B1 (CYP1B1) is a universal cancer marker and is implicated in many other disorders. Mutations in CYP1B1 are also associated with childhood blindness due to primary congenital glaucoma (PCG). To understand the CYP1B1 mediated etiopathology of PCG and pathomechanism of various cancers, it is important to carry out its functional studies. Heterologous expression of CYP1B1 in prokaryotes is imperative because bacteria yield a higher amount of heterologous proteins in lesser time and so the expressed protein is ideal for functional studies. In such expression system there is no interference by other eukaryotic proteins. But the story is not that simple as expression of heterologous CYP1B1 poses many technical difficulties. Investigators have employed various modifications/deletions of CYP N-terminus to improve CYP1B1 expression. However, the drawback of these studies is that it changes the original protein and, as a result, invalidates functional studies. The present study examines the role of various conditions and reagents in successful and consistent expression of sufficient quantities of unmodified/native human CYP1B1 in E. coli. We aimed at expressing CYP1B1 in various strains of E. coli and in the course developed a protocol that results in high expression of unmodified protein sufficient for functional/biophysical studies. We examined CYP1B1 expression with respect to different expression vectors, bacterial strains, types of culture media, time, Isopropyl β-D-1-thiogalactopyranoside concentrations, temperatures, rotations per minute, conditioning reagents and the efficacy of a newly described technique called double colony selection. We report a protocol that is simple, easy and can be carried out in any laboratory without the requirement of a fermentor. Though employed for CYP1B1 expression, this protocol can ideally be used to express any eukaryotic membrane protein.