Identification of a novel MYOC mutation in a Chinese family with primary open-angle glaucoma

Asian Race and Primary Open-Angle Glaucoma: Where Do We Stand?

Primary open-angle glaucoma (POAG) is an optic neuropathy characterized by irreversible retinal ganglion cell damage and visual field loss. The global POAG prevalence is estimated to be 3.05%, and near term is expected to significantly rise, especially within aging Asian populations. Primary angle-closure glaucoma disproportionately affects Asians, with up to four times greater prevalence of normal-tension glaucoma reported compared with high-tension glaucoma. Estimates for overall POAG prevalence in Asian populations vary, with Chinese and Indian populations representing the majority of future cases. Structural characteristics associated with glaucoma progression including the optic nerve head, retina, and cornea are distinct in Asians, serving as intermediates between African and European descent populations. Patterns in IOP suggest some similarities between races, with a significant inverse relationship between age and IOP only in Asian populations. Genetic differences have been suggested to play a role in these differences, however, a clear genetic pattern is yet to be established. POAG pathogenesis differs between Asians and other ethnicities, and it may differ within the broad classification of the Asian race. Greater awareness and further research are needed to improve treatment plans and outcomes for the increasingly high prevalence of normal tension glaucoma within aging Asian populations.

Penetrance of MYOC gene mutation in primary open-angle glaucoma: A systematic review and meta-analysis

PURPOSE

To investigate the penetrance of MYOC gene mutation in primary open-angle glaucoma (POAG) through systematic review and meta-analysis. To explore the factors affecting the penetrance of MYOC and provide evidence-based medical evidence for clinical work.

METHODS

We searched all studies that reported the penetrance of MYOC mutation in PubMed, Embase, Web of Science, and Chinese databases including Wanfang, CNKI (China National Knowledge Infrastructure), and CBM (China Bio-Med). Random effects meta-analysis was conducted to estimate the penetrance of MYOC mutation in POAG.

RESULTS

Fifty-two studies were included in this analysis after screening. Meta-analysis of the penetrance of MYOC mutation showed that the penetrance of MYOC mutation in POAG was 60% (95% CI: 51.0% to 68.0%) and the penetrance of MYOC mutation in POAG and suspected POAG was 68% (95% CI: 60.0% to 75.0%). The penetrance of MYOC mutation increases with age. Among Caucasians, Asians, and Africans, the penetrance of MYOC mutation in POAG was 55%, 71%, 54%, respectively, and the penetrance of MYOC mutation in POAG and suspected POAG was 64%, 83%, and 57%, respectively. Besides, the penetrance of different MYOC mutation sites was significantly discrepant. The penetrance of MYOC mutation in POAG ranged from 10.3% to 100% depending on the mutation sites. Some MYOC mutation sites have a certain population specificity, which is only pathogenic in Caucasians or Asians.

CONCLUSIONS

The penetrance of MYOC mutation in POAG showed significant differences due to different mutation sites. The penetrance increased with the accrescent of age. Ethnic difference was an important factor affecting the penetrance of MYOC mutation. Knowing the rules and influencing factors of the penetrance of MYOC mutations is significant for the assessment of the risk of POAG in carriers with the MYOC mutation.

Common and rare myocilin variants: Predicting glaucoma pathogenicity based on genetics, clinical, and laboratory misfolding data

Rare variants of the olfactomedin domain of myocilin are considered causative for inherited, early-onset open-angle glaucoma, with a misfolding toxic gain-of-function pathogenic mechanism detailed by 20 years of laboratory research. Myocilin variants are documented in the scientific literature and identified through large-scale genetic sequencing projects such as those curated in the Genome Aggregation Database (gnomAD). In the absence of key clinical and laboratory information, however, the pathogenicity of any given variant is not clear, because glaucoma is a heterogeneous and prevalent age-onset disease, and common variants are likely benign. In this review, we reevaluate the likelihood of pathogenicity for the ~100 nonsynonymous missense, insertion-deletion, and premature termination of myocilin olfactomedin variants documented in the literature. We integrate available clinical, laboratory cellular, biochemical and biophysical data, the olfactomedin domain structure, and population genetics data from gnomAD. Of the variants inspected, ~50% can be binned based on a preponderance of data, leaving many of uncertain pathogenicity that motivate additional studies. Ultimately, the approach of combining metrics from different disciplines will likely resolve outstanding complexities regarding the role of this misfolding-prone protein within the context of a multifactorial and prevalent ocular disease, and pave the way for new precision medicine therapeutics.

Systemic Genotype-Phenotype Analysis of MYOC Variants Based on Exome Sequencing and Literature Review

PURPOSE

This study aims to characterize disease-causing variants in the myocilin gene (MYOC), which is associated with autosomal dominant primary open-angle glaucoma (adPOAG).

DESIGN

Case-control study.

METHODS

MYOC variants were collected from in-house exome sequencing data of 7092 individuals. Genotype-phenotype analysis and bioinformatics evaluation were used to distinguish potential pathogenic variants for POAG from others. MYOC mutations in published works of literature were also systemically analyzed.

RESULTS

In total, 53 variants in MYOC were detected in the 7092 subjects, including 45 rare variants (MAF < 0.01) and 8 polymorphisms (MAF ≥ 0.01), or 48 missense variants and 5 truncation variants. There was no difference in the frequency of the 8 polymorphisms between subjects with and without POAG (P > 0.05). The total number of rare MYOC variants was significantly higher in POAG than that in in-house controls (P = 3.31E-14). The pathogenic/likely pathogenic variants (p.P254T, p.S341P, p.G367R, p.P370L, p.D378G, p.C433Y, and p.L486F) were exclusively present in 8 POAG but absent in in-house controls (P = 2.79E-10). Rare truncation MYOC variants were not enriched in POAG as compared with those in in-house controls (P = 0.28). Further analysis of previously reported MYOC variants suggested that pathogenic/likely pathogenic variants were enriched in the conserved olfactomedin domain. Truncation MYOC variants were scattered in the coding region, where only p.Q368∗ had relatively strong evidence to be causative for adPOAG, whereas most others are questionable.

CONCLUSIONS

Most MYOC variants contributing to adPOAG could be characterized as rare missense variants located in OLF-domain and predicted to be damaging through multiple tools. The effect of other variants, especially for truncation variants (except for p.Q368∗) need further clarification.

Physiological function of myocilin and its role in the pathogenesis of glaucoma in the trabecular meshwork (Review)

Myocilin is highly expressed in the trabecular meshwork (TM), which plays an important role in the regulation of intraocular pressure (IOP). Myocilin abnormalities may cause dysfunction of the TM, potentially leading to increased IOP. High IOP is a well‑known primary risk factor for glaucoma. Myocilin mutations are common among glaucoma patients, and they are implicated in juvenile‑onset open‑angle glaucoma (JOAG) and adult‑onset primary open‑angle glaucoma (POAG). Aggregation of aberrant mutant myocilins is closely associated with glaucoma pathogenesis. The aim of the present review was to discuss the recent findings regarding the major physiological functions of myocilin, such as intra‑ and extracellular proteolytic processes. We also aimed to discuss the risk factors associated with myocilin and the development of glaucoma, such as misfolded/mutant myocilin, imbalance of myocilin and extracellular proteins, and instability of mutant myocilin associated with temperature. Finally, we further outlined certain issues that are yet to be resolved, which may represent the basis for future studies on the role of myocilin in glaucoma.

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

Background

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

Case presentation

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

Conclusion

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

Novel Compound Heterozygous CBS Mutations Cause Homocystinuria in a Han Chinese Family

The cystathionine β-synthase (CBS) gene has been shown to be related to homocystinuria. This study was aimed to detect the mutations in CBS in a Han Chinese family with homocystinuria. A four-generation family from Shandong Province of China was recruited in this study. All available members of the family underwent comprehensive medical examinations. Genomic DNA was collected from peripheral blood of all the participants. The coding sequence of CBS was amplified by polymerase chain reaction (PCR), followed by direct DNA sequencing. Among all the family members, three affected individuals showed typical clinical features of homocystinuria. Two novel compound heterozygous mutations in the CBS gene, c.407T > C (p. L136P) and c.473C > T (p.A158V), were identified by sequencing analysis in this family. Both of the two missense mutations were detected in the three patients. Other available normal individuals, including the patients' parents, grand parents, her younger sister and brother in this family either carried one of the two mutations, or none. In addition, the two mutations were not found in 600 ethnically matched normal controls. This study provides a mutation spectrum of CBS resulting in homocystinuriain a Chinese population, which may shed light on the molecular pathogenesis and clinical diagnosis of CBS-associated homocystinuria.