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PubMed This is a summary of 18 peer-reviewed journal articles Updated
Ophthalmology · Glaucoma 1, Open-Angle, A

The Biology of GLC1A: Proteins, Cellular Stress, and Genes

At a Glance

GLC1A is an inherited form of open-angle glaucoma in which disease-causing MYOC changes can produce misfolded myocilin that stresses eye drainage cells. This can reduce fluid outflow and raise eye pressure, but risk and age of onset vary by variant.

To understand GLC1A, it helps to look inside the microscopic drainage system of the eye. While many forms of glaucoma are caused by unknown factors, researchers have identified a very specific biological mechanism in MYOC-associated glaucoma [1]. By understanding this mechanism, you can better appreciate why early treatment is so effective at protecting your vision.

The “Toxic Gain of Function”

Your body’s cells are like small factories that produce proteins. The MYOC gene provides the instructions for making a protein called myocilin [2]. In a healthy eye, this protein is created and then sent out of the cells in the trabecular meshwork (the eye’s primary drain) to help maintain fluid balance [1].

When a pathogenic MYOC mutation is present, the “factory” begins producing a “misfolded” or broken version of the protein [3]. This leads to a process called toxic gain of function [1]:

  • Cellular Accumulation: Instead of leaving the cell, these misfolded proteins are retained and accumulate inside the cell [1][4].
  • Cellular Traffic Jam: These misfolded proteins get stuck in a part of the cell called the endoplasmic reticulum (ER), which is responsible for folding and transporting proteins [1].
  • ER Stress: The buildup causes ER stress [5]. The cell triggers an emergency response. Over time, this chronic stress can damage or even kill the vital cells in the eye’s drain [6][7].
  • Reduced Outflow: As these drainage cells become dysfunctional, the fluid in your eye (aqueous humor) cannot exit as easily as it should. This causes the intraocular pressure (IOP) to rise, which can eventually damage the optic nerve [8][9].

Passing It On: Autosomal Dominant Inheritance

GLC1A follows an autosomal dominant pattern of inheritance [10]. Here is what that means for your family:

  • 50% Probability: If you carry one copy of the mutated gene, there is a 50% (1 in 2) chance of passing that same mutation to each of your children [11].
  • Gender-Neutral: The mutation can be passed from either a mother or a father and can affect both sons and daughters equally.
  • Apparent “Skipped” Generations: While dominant conditions are usually seen in every generation, incomplete penetrance, very late onset, unrecognized mild disease, or occasional de novo (new) mutations can make a family history appear to skip a generation [10].

Understanding Penetrance: Risk vs. Certainty

Carrying a MYOC mutation does not automatically mean you will develop severe glaucoma. Doctors use the term penetrance to describe how likely it is that a person with a specific gene change will actually show symptoms of the disease [12].

Penetrance in GLC1A is “incomplete,” meaning some people carry the gene but never develop high pressure or vision loss [13]. The average penetrance varies substantially by exact variant, age, ancestry, and the family studied [12]. However, this risk is age-dependent; the older a carrier gets, the more likely they are to develop signs of the condition [14].

Not All Mutations Are the Same

There are many different “flavors” or variants of the MYOC mutation, and they can behave very differently [12]:

  • Q368X: This is the most common MYOC mutation [13]. It often has lower, age-dependent penetrance, meaning people who have it may develop only mildly elevated pressure or may not show symptoms until much later in life [13][15].
  • G367R: In contrast, this variant is often more aggressive. It is frequently associated with early onset and can have very high penetrance (up to 90% in some specific families studied), causing symptoms to appear in childhood or early adulthood (Juvenile Open-Angle Glaucoma) [16][14].

Knowing your specific variant helps your doctor anticipate whether your glaucoma might be fast-moving or slow-moving, allowing them to tailor your treatment plan to your unique genetic profile [17]. No matter which variant you have, the biological goal remains the same: lowering the pressure to protect your optic nerve from the effects of the cellular dysfunction [18].

Common questions in this guide

How does a MYOC mutation lead to GLC1A glaucoma?
A disease-causing MYOC change can make a misfolded form of the myocilin protein that becomes trapped inside cells in the eye’s drainage tissue, called the trabecular meshwork. The resulting cell stress and damage can reduce fluid drainage, raise eye pressure, and eventually harm the optic nerve.
If I carry GLC1A, will I definitely develop glaucoma?
No. GLC1A has incomplete, age-dependent penetrance, so some people with a MYOC mutation never develop high eye pressure or vision loss. The likelihood can differ with the exact variant, age, ancestry, and family being studied.
How is MYOC-related glaucoma passed through a family?
GLC1A is usually inherited in an autosomal dominant pattern. A person with one disease-causing copy of the MYOC gene has a 1-in-2 chance of passing it to each child, and the risk is the same for sons and daughters. A family history can appear to skip a generation because penetrance is incomplete, disease may start late or be mild, or a new mutation may occur.
Which MYOC variants may cause earlier or more severe disease?
Q368X is a common MYOC variant and often has lower, age-dependent penetrance, while G367R is more often linked with early-onset disease and high penetrance in some families. G367R can be associated with juvenile open-angle glaucoma. Your exact variant should be interpreted by your eye doctor or genetic counselor.
Why does the exact MYOC variant matter for my care?
Different MYOC variants can differ in typical age of onset, penetrance, and pace of disease. Knowing the variant may help your clinician plan eye-pressure monitoring and decide how closely to follow or treat you. It does not predict your individual course with certainty.
How can treatment help protect vision in GLC1A?
The main treatment goal is to lower eye pressure so the optic nerve is protected from damage caused by reduced fluid drainage. Follow the pressure-lowering plan prescribed by your eye doctor, which may include eye drops, and ask what target pressure is appropriate for you. Early treatment and regular monitoring are important.
Should relatives consider genetic testing or eye screening?
A genetic counselor can help your family discuss cascade testing for the specific MYOC variant. Relatives may also need eye-pressure screening, with timing based on the variant, family history, and advice from an eye-care professional.

Questions For You

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Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.What is the exact name of my MYOC mutation (e.g., Q368X or G367R), and what does the medical literature say about its typical age of onset?
  2. 2.Is my variant classified as 'pathogenic' or 'likely pathogenic,' and how does that change my monitoring plan?
  3. 3.Given this mutation, what is my specific 'target pressure' for my eyes?
  4. 4.Should my family members see a genetic counselor to discuss 'cascade testing' for this specific gene?

References

References (18)
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    Myocilin misfolding and glaucoma: A 20-year update.

    Saccuzzo EG, Youngblood HA, Lieberman RL

    Progress in retinal and eye research 2023; (95()):101188 doi:10.1016/j.preteyeres.2023.101188.

    PMID: 37217093
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    Identification of Mutations in Myocilin and Beta-1,4-galactosyltransferase 3 Genes in a Chinese Family with Primary Open-angle Glaucoma.

    Liao RF, Zhong ZL, Ye MJ, et al.

    Chinese medical journal 2016; (129(23)):2810-2815 doi:10.4103/0366-6999.194641.

    PMID: 27900994
  3. 3

    Molecular Insights into Myocilin and Its Glaucoma-Causing Misfolded Olfactomedin Domain Variants.

    Lieberman RL, Ma MT

    Accounts of chemical research 2021; (54(9)):2205-2215 doi:10.1021/acs.accounts.1c00060.

    PMID: 33847483
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    Different Grp94 components interact transiently with the myocilin olfactomedin domain in vitro to enhance or retard its amyloid aggregation.

    Huard DJE, Jonke AP, Torres MP, Lieberman RL

    Scientific reports 2019; (9(1)):12769 doi:10.1038/s41598-019-48751-8.

    PMID: 31484937
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    Methods for Analyzing Endoplasmic Reticulum Stress in the Trabecular Meshwork of Glaucoma Models.

    Maddineni P, Kasetti RB, Zode GS

    Methods in molecular biology (Clifton, N.J.) 2018; (1695()):121-134 doi:10.1007/978-1-4939-7407-8_12.

    PMID: 29190024
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    Accumulation of Asn450Tyr mutant myocilin in ER promotes apoptosis of human trabecular meshwork cells.

    Yan X, Wu S, Liu Q, et al.

    Molecular vision 2020; (26()):563-573.

    PMID: 32818018
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    A Histologic Categorization of Aqueous Outflow Routes in Familial Open-Angle Glaucoma and Associations With Mutations in the MYOC Gene in Japanese Patients.

    Hamanaka T, Kimura M, Sakurai T, et al.

    Investigative ophthalmology & visual science 2017; (58(5)):2818-2831 doi:10.1167/iovs.16-20646.

    PMID: 28564705
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    Expression of Mutant Myocilin Induces Abnormal Intracellular Accumulation of Selected Extracellular Matrix Proteins in the Trabecular Meshwork.

    Kasetti RB, Phan TN, Millar JC, Zode GS

    Investigative ophthalmology & visual science 2016; (57(14)):6058-6069 doi:10.1167/iovs.16-19610.

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    CRISPR-Cas9-based treatment of myocilin-associated glaucoma.

    Jain A, Zode G, Kasetti RB, et al.

    Proceedings of the National Academy of Sciences of the United States of America 2017; (114(42)):11199-11204 doi:10.1073/pnas.1706193114.

    PMID: 28973933
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    A novel de novo Myocilin variant in a patient with sporadic juvenile open angle glaucoma.

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    BMC medical genetics 2016; (17()):30 doi:10.1186/s12881-016-0291-5.

    PMID: 27080696
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    Systemic Genotype-Phenotype Analysis of MYOC Variants Based on Exome Sequencing and Literature Review.

    Li X, Xiao X, Li S, et al.

    Asia-Pacific journal of ophthalmology (Philadelphia, Pa.) 2021; (10(2)):173-182 doi:10.1097/APO.0000000000000382.

    PMID: 33793440
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    Penetrance of MYOC gene mutation in primary open-angle glaucoma: A systematic review and meta-analysis.

    Xie JJ, Zhang GW, Cui HY, et al.

    Ophthalmic genetics 2022; (43(2)):240-247 doi:10.1080/13816810.2021.2021427.

    PMID: 35014583
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    Myocilin Gene Gln368Ter Variant Penetrance and Association With Glaucoma in Population-Based and Registry-Based Studies.

    Han X, Souzeau E, Ong JS, et al.

    JAMA ophthalmology 2019; (137(1)):28-35 doi:10.1001/jamaophthalmol.2018.4477.

    PMID: 30267046
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    The clinical feature of myocilin Y437H mutation in a Chinese family with primary open-angle glaucoma.

    Lei L, Li S, Liu X, Zhang C

    The British journal of ophthalmology 2019; (103(10)):1524-1529 doi:10.1136/bjophthalmol-2018-313069.

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    Characteristics of p.Gln368Ter Myocilin Variant and Influence of Polygenic Risk on Glaucoma Penetrance in the UK Biobank.

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    PMID: 33713785
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    The mutational spectrum of Myocilin gene among familial versus sporadic cases of Juvenile onset open angle glaucoma.

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    Therapeutic mRNA delivery of CRISPR-Cas9 to the trabecular meshwork reverses ocular hypertension in myocilin glaucoma.

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This page explains the genetic biology of GLC1A for informational purposes only and does not constitute medical advice. An ophthalmologist and genetic counselor can interpret your MYOC variant, eye-pressure risk, and screening needs.