Genotype-Phenotype Correlation in Moroccan Patients With Primary Congenital Glaucoma:

Next-generation sequencing-based gene panel tests for the detection of rare variants and hypomorphic alleles associated with primary open-angle glaucoma

Primary open-angle glaucoma (POAG) is a complex disease with a strong hereditably component. Several genetic variants have recently been associated with POAG, partially due to technological improvements such as next-generation sequencing (NGS). The aim of this study was to genetically analyze patients with POAG to determine the contribution of rare variants and hypomorphic alleles associated with glaucoma as a future method of diagnosis and early treatment. Seventy-two genes potentially associated with adult glaucoma were studied in 61 patients with POAG. Additionally, we sequenced the coding sequence of CYP1B1 gene in 13 independent patients to deep analyze the potential association of hypomorphic CYP1B1 alleles in the pathogenesis of POAG. We detected nine rare variants in 16% of POAG patients studied by NGS. Those rare variants are located in CYP1B1, SIX6, CARD10, MFN1, OPTC, OPTN, and WDR36 glaucoma-related genes. Hypomorphic variants in CYP1B1 and SIX6 genes have been identified in 8% of the total POAG patient assessed. Our findings suggest that NGS could be a valuable tool to clarify the impact of genetic component on adult glaucoma. However, in order to demonstrate the contribution of these rare variants and hypomorphic alleles to glaucoma, segregation and functional studies would be necessary. The identification of new variants and hypomorphic alleles in glaucoma patients will help to configure the genetic identity of these patients, in order to make an early and precise molecular diagnosis.

Genetics and Glaucoma: the state of the art

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

Pediatric Glaucoma-From Screening, Early Detection to Management

Pediatric glaucoma (PG) covers a rare and heterogeneous group of diseases with variable causes and presentations. Delayed diagnosis of PG could lead to blindness, bringing emotional and psychological burdens to patients' caregivers. Recent genetic studies identified novel causative genes, which may provide new insight into the etiology of PG. More effective screening strategies could be beneficial for timely diagnosis and treatment. New findings on clinical characteristics and the latest examination instruments have provided additional evidence for diagnosing PG. In addition to IOP-lowering therapy, managing concomitant amblyopia and other associated ocular pathologies is essential to achieve a better visual outcome. Surgical treatment is usually required although medication is often used before surgery. These include angle surgeries, filtering surgeries, minimally invasive glaucoma surgeries, cyclophotocoagulation, and deep sclerectomy. Several advanced surgical therapies have been developed to increase success rates and decrease postoperative complications. Here, we review the classification and diagnosis, etiology, screening, clinical characteristics, examinations, and management of PG.

Neonatal-Onset Congenital Ectropion Uveae May Be Caused by a Distinct CYP1B1 Pathologic Variant

PURPOSE

To report underlying genetic variants of recently described distinct phenotype of newborn glaucoma: neonatal-onset congenital ectropion uveae (NO-CEU).

DESIGN

Prospective cohort study.

METHODS

Setting: tertiary care teaching institute.

SUBJECTS

Thirteen children with clinical diagnosis of NO-CEU who had completed 1-year follow-up after glaucoma surgery and had undergone clinical exome sequencing (CES) by selective capture and sequencing of the protein-coding regions of the genes including 19 candidate genes for NO-CEU were assessed. The same criteria were applied for evaluating pathogenicity of variants to all the candidate genes.

OUTCOME MEASURES

primary-genetic variants found on CES keeping in view the clinical indication of congenital glaucoma; secondary-corneal clarity and intraocular pressure (IOP) at baseline and 1-year follow-up, interventions required to control IOP, and postoperative visual acuity. The genetic variants were correlated with the outcome.

RESULTS

All 13 patients diagnosed with NO-CEU had onset of glaucoma at birth and severe bilateral disease. Twelve of 13 (92.3%) patients harbored CYP1B1 variants. Nine of these 12 patients (83.3%) were homozygous for [c.1169G>A(p.Arg390His)] in exon-3 of CYP1B, with 5 common homozygous single-nucleotide polymorphisms flanking the pathogenic variant. They had intractable glaucoma and required multiple surgeries. Six patients had persistent corneal opacities, necessitating optical iridectomies. Three patients were compound heterozygous for CYP1B1 variants, showing [c.1169G>A(p.Arg390His)] along with [c.1103G>A(p.Arg368His)], [c.1103G>A (p.Arg368His)] along with [c.1403_1429dup(p.Arg468_Ser476dup)], and [(c.1063C>T(p.Arg355Ter)] along with [c.1325del(p.Pro442GlnfsTer15)]. These patients had better visual outcomes.

CONCLUSIONS

NO-CEU appears to be a phenotypic marker for specific CYP1B1 genotypes, one of which is [c.1169G>A(p.Arg390His)] in our study population. Phenotype recognition is helpful to characterize the underlying genetic variants.

Geographical Variability in CYP1B1 Mutations in Primary Congenital Glaucoma

Primary congenital glaucoma (PCG) is a rare type of glaucoma that is inherited in an autosomal recessive manner. PCG can lead to blindness if not detected early in children aged 3 or younger. PCG varies in presentation among various populations, where disease presentation and disease severity vary by mutation. The most common gene implicated in PCG is cytochrome p450 1B1 (CYP1B1). Here, we sought to review the literature for mutations in CYP1B1 and their presentation among different populations. Areas of interest include recent findings on disease presentation and potential implications on our understanding of PCG pathophysiology.

First Results from the Prospective German Registry for Childhood Glaucoma: Phenotype-Genotype Association

Childhood glaucoma is a heterogeneous disease and can be associated with various genetic alterations. The aim of this study was to report first results of the phenotype–genotype relationship in a German childhood glaucoma cohort. Forty-nine eyes of 29 children diagnosed with childhood glaucoma were prospectively included in the registry. Besides medical history, non-genetic risk factor anamnesis and examination results, genetic examination report was obtained (23 cases). DNA from peripheral blood or buccal swab was used for molecular genetic analysis using a specific glaucoma gene panel. Primary endpoint was the distribution of causative genetic mutations and associated disorders. Median age was 1.8 (IQR 0.6; 3.8) years, 64% participants were female. Secondary childhood glaucoma (55%) was more common than primary childhood glaucoma (41%). In 14%, parental consanguinity was indicated. A mutation was found in all these cases, which makes consanguinity an important risk factor for genetic causes in childhood glaucoma. CYP1B1 (30%) and TEK (10%) mutations were found in primary childhood glaucoma patients. In secondary childhood glaucoma cases, alterations in CYP1B1 (25%), SOX11 (13%), FOXC1 (13%), GJA8 (13%) and LTBP2 (13%) were detected. Congenital cataract was associated with variants in FYCO1 and CRYBB3 (25% each), and one case of primary megalocornea with a CHRDL1 aberration. Novel variants of causative genetic mutations were found. Distribution of childhood glaucoma types and causative genes was comparable to previous investigated cohorts. This is the first prospective study using standardized forms to determine phenotypes and non-genetic factors in childhood glaucoma with the aim to evaluate their association with genotypes in childhood glaucoma.

Genetics in primary congenital glaucoma: Implications in disease management and counseling

Primary congenital glaucoma is an important cause of visual impairment in children. It can develop both pre- and postnatally. Angle surgery is the first line treatment modality. If the disease remains untreated or if the diagnosis is delayed, it can lead to irreversible visual loss and blindness. The genetics of primary congenital glaucoma are complex and not yet entirely understood. At present multiple disease-causing genes have been identified. CYP1B1 is the most well known gene causing autosomal recessive congenital glaucoma. Other genes have been found to play a role through recessive, dominant or polygenic mechanisms. Here we provide an overview of the known genes and mechanisms described in patients with PCG. Furthermore, we provide a practical counseling and follow-up guideline for relatives of a proband.

Meta-analysis of CYP1B1 gene mutations in primary congenital glaucoma patients

Primary congenital glaucoma (PCG) is a rare and severe form of glaucoma and is usually transmitted as an autosomal-recessive disease. However, PCG is more common in certain ethnic and geographic groups where consanguineous relationships are common. The importance of this review is to inspect the mutations in the cytochrome P450 1B1 gene (CYP1B1) and to highlight the interest of the genetic study of CYP1B1 mutations. An in-depth study was carried out by the following search engines: PubMed, Scopus, clinic key and direct science for articles that have been published from 2011 until 2020. One hundred and sixty-one mutations were found in 1641 tested patients and three families, including 78 novel mutations. We identified a no significant difference in the sex ratio and the bilaterality was reported in the majority of patients. We have shown through this study that inbreeding plays an important role in the pathogenesis of PCG transmission compared to the sporadic mutations that have been found in some cases. The majority of the included studies were from ASIA (64.3%), followed by Europe (17.85%), America (10.71%) and Africa (7.14%). The first and most common mutation in our study is 182 G>A (p.Gly61Glu). It was identified in Iran, Portugal and Saudi Arabia and for the first time in Brazil and Vietnam. The greatest number of mutations in common is p.Gly61Glu. Mainly within five countries: Iran, Portugal, Saudi Arabia, Brazil and Vietnam. The first step in PCG screening should be a genetic test looking for founder and common mutation coupled with a clinical examination.

Genetic Epidemiology of Primary Congenital Glaucoma in the 22 Arab Countries: A Systematic Review

PURPOSE

Primary congenital glaucoma (PCG) is a rare glaucoma type that develops in early infantile period and contributes to an elevated pressure on ocular cavity. Variants in CYP1B1 gene are the most encountered in PCG cases. The prevalence of PCG is relatively high among Arabs, however its genetic epidemiology remains understudied. This study aims to systematically identify all reported PCG disease-causing variants in the Arab population and investigate their potential genotype-phenotype correlations.

METHODS

We searched four different databases (PubMed, ScienceDirect, Google Scholar, and Scopus) from the time of inception until July 2020. Broad search terms were used to capture all possible information about the genetic epidemiology of PCG among Arabs.

RESULTS

We identified a total of 77 disease-causing variants in 361 patients and 88 families; of these, 33 were unique to Arabs. Sixty-nine variants were identified in the CYP1B1 gene, five variants were in the MYOC gene and single variants were reported in NTF4, FOXC1, and WDR36 genes. The most common reported variant was the c.182 G > A in the CYP1B1 gene. All identified variants were from ten Arab Countries (Saudi Arabia, Kuwait, Oman, Egypt, Morocco, Lebanon, Tunisia, Iraq, Algeria, and Mauritania). We identified 44 shared variants with other ethnicities demonstrated a distinctive genotype-phenotype correlation. Consanguinity was observed in the majority of Arab PCG patients, ranging from 45% to 100%.

CONCLUSION

PCG causing variants were identified in 10 Arab countries, which were mostly detected in the CYB1P1 gene. Arab patients with PCG seem to have distinctive genotype-phenotype correlations.

Two novel variants in CYP1B1 gene: a major contributor of autosomal recessive primary congenital glaucoma with allelic heterogeneity in Pakistani patients

AIM

To find the CYP1B1 mutations associated with primary congenital glaucoma (PCG) in Pakistani consanguineous pedigrees.

METHODS

After getting informed consent, 11 consanguineous pedigrees belonging to different ethnic groups were enrolled. Detailed medical history was recorded and pedigrees were drawn. The standard ophthalmological examination was done to characterize the phenotype. Genomic DNA was extracted from 10 mL whole blood and coding exons and exon intron boundaries of CYP1B1 gene were directly sequenced. Bioinformatics tools were used to model the mutant protein and predict the effect of novel variants on protein structure and function.

RESULTS

Sequencing analysis revealed 5 different CYP1B1 variants in 7 families (7/11; 64%), including two novel variants. A common mutation, p.R390H was found in four families, whereas p.P437L was found once in a family. Two novel variants, a homozygous non sense variant p.L13* and a compound heterozygous variant, p.P350T along with p.V364M were segregating with PCG in two families. All the patients had the variable onset and severity of the disease. The success rate of early clinical interventions was observed dependent on mutation types and position. Two different haplotypes were associated with frequently found mutation, p.R390H.

CONCLUSION

Identification of novel CYP1B1 variants reassert the genetic heterogeneity of Pakistani PCG patients. The patients with missense mutations show severe phenotypic presentations and poor vision after surgical interventions as compare to patients with null variants. This may help to better understand the role of CYP1B1 mutations in the development of PCG and its course of pathogenicity.

Analysis of CYP1B1 Gene Mutations in Patients with Primary Congenital Glaucoma

Primary congenital glaucoma (PCG) is the most common type of infantile glaucoma, yet it remains a relatively rare disease, because the disease is often transmitted in an autosomal recessive pattern. However, PCG occurs up to 10 times more frequently in certain ethnic and geographical groups where consanguineous relationships are common. The aim of this study was to investigate the distribution of mutations in the cytochrome P450 1B1 gene ( CYP1B1 ) in patients with PCG among different populations around the world from 2011 until May 2016. We referred to the electronic databases, such as Medline, Clinicalkey, Scopus, and ScienceDirect, to search for articles that were published in this area. Nineteen records were included in this qualitative synthesis. CYP1B1 mutations were assessed in 1,220 patients with PCG and identified in 41.6% of them. According to these studies, 99 mutations including 60 novel mutations were found. Nonsignificant difference in the sex ratio has been reported. This current review shows that consanguinity plays an important role in the PCG pathogenesis and transmission; however, sporadic mutations have been found in some cases. A difference in penetrance was highlighted by some mutations. The CYP1B1 mutations were mostly found in the Middle East and the Maghreb with a rate of 64.8 and 54.4%, respectively, followed by Europe (34.7%), Asia (21.3%), and finally the United States (14.9%). Founder mutations in different geographical areas have been discovered. For instance, the p.Gly61Glu, p.Arg390His, p.Gly61Glu, c.4,339delG, p.E387Lys, and p.Val320Leu were considered founder mutations for Iran/Saudi Arabia, Pakistan, Lebanon, Morocco, Europe, and Vietnam/South Korea, respectively. Many common mutations in different countries were found, such as in Morocco, where its mutations were similar to seven other countries. These findings suggest that the ethnic differences and the geographical distribution of PCG give us a large CYP1B1 mutation pattern. Genetic tests looking for founder and common mutations should be the first step in genetic screening for patients with PCG.