The CLDN18 gene helps make a protein that forms tight seals between neighboring cells, especially in the stomach lining and parts of the lungs. If it does not work as it should, these protective barriers can become less effective, which may irritate tissue and contribute to disease. Some changes involving the CLDN18 gene are linked to certain cancers, particularly stomach cancer, often when the gene becomes abnormally active or joins with another gene. This gene plays an important role in keeping delicate lining tissues stable and protected.
What is a gene?
Genes are stretches of DNA that hold instructions your cells use to make molecules or manage processes throughout the body. Some genes provide the directions for producing proteins, which are the parts of cells that do much of the work. Others mainly regulate when certain processes happen, where they happen, and how active they are. Taken together, genes affect how your body grows and works, and they can influence how you respond to food, stress, and medications. For a deeper look at this topic, you can read more in the LearnHub.
Overview
CLDN18Gene function
What if the gene works
The CLDN18 gene helps make claudin 18, a protein that helps seal neighboring cells together. It supports the protective lining of the stomach and parts of the lungs, helping control what passes between cells.
Risk
What if the gene does not work
Milder CLDN18 variants may only partly weaken tight junctions, while more severe variants can cause greater loss of the stomach and lung cell barrier. This can let acid, ions, and other small molecules leak between neighboring cells.
Treatment
What does that mean for your treatment
No CLDN18-specific treatment or drug choice approach is currently established for pathogenic or loss-of-function variants in the CLDN18 gene. Separately, CLDN18.2 protein expression in some stomach and gastroesophageal cancers can guide use of zolbetuximab, so the CLDN18 gene is an established cancer biomarker and drug target in that setting.
Gene function
What if the gene works
In your body, the CLDN18 gene helps neighboring cells form snug seals in important linings, especially the stomach and the tiny air sacs in the lungs. These seals help control what passes between cells instead of through them. Understanding how the CLDN18 gene works can make it easier to see how tissues keep a steady, protective surface.
The CLDN18 gene helps make tight junctions, which are seal-like links between neighboring cells. These links let cells sit close together and form neat, continuous sheets.
Its protein helps control what slips through the spaces between cells, including water, salts, and other small substances. This gives tissues a more selective barrier and supports the body’s day-to-day balance.
In the stomach lining and lung air sacs, the CLDN18 gene helps keep the cell surface organized and protective. This supports tissue stability where cells need to hold a careful boundary with the outside world.
What is a variant?
A genetic variant is a minor change in the DNA sequence within a gene. These changes are common and are part of normal human diversity, including differences in appearance, metabolism, and how the body responds to environmental influences. Many variants do not cause any noticeable effect and simply represent natural genetic variation. Sometimes, though, a variant changes how a gene works more substantially and may contribute to or cause a genetic condition.
Genetic variants
What if the gene does not work
Variants in the CLDN18 gene can change how the claudin-18 protein is built, so it may fold poorly, be unstable, or fail to reach the tight seals between neighboring cells. In practical terms, this is how CLDN18 gene variants affect cell barriers at a microscopic level. Milder variants may partly weaken the protein’s shape or partner binding, while more severe variants can truncate the protein or stop it from being made at all.
How variants are linked to conditions
Research on health conditions linked to CLDN18 gene variants is still developing, and CLDN18 does not yet have a broadly confirmed link to one specific inherited condition. If you have a reported CLDN18 variant or a CLDN18-related diagnosis, your doctor or genetic counselor can explain what it may mean for you based on your own results and health history.
A variant is not necessarily a diagnosis
Genetic variants are a usual feature of human biology and are widespread across the general population. Most do not directly affect health and instead reflect normal human diversity. For many genes, a variant associated with a condition points to a possible link rather than a confirmed diagnosis, particularly when several genes and environmental influences play a role. In other situations, one well-characterized variant in a particular gene is enough to confirm a diagnosis.
Are there things that can increase or change my risk?
There is not yet broadly confirmed evidence on specific factors that increase or reduce health risk related to the CLDN18 gene itself. If CLDN18 comes up in your test results, the meaning often depends on the exact change and the health condition being looked at, so personal guidance from a doctor or genetic counselor is important.
Inheritance of CLDN18 variants
There is not yet a broadly confirmed disease inheritance pattern for CLDN18 that applies across a specific, well-established CLDN18-related condition, so answers to how CLDN18 gene variants are inherited remain cautious and may evolve with research. The CLDN18 gene is located on chromosome 3, which is an autosome. That means a person inherits one copy of this gene from each parent, regardless of sex.
What does my CLDN18 result mean for my family?
There is not yet a broadly confirmed inheritance pattern tied to a specific condition for CLDN18 in the way there is for some other genes. If you have a specific CLDN18 result and want to understand what it could mean for your relatives, a doctor or genetic counselor can explain it in the context of your family history and the exact result.
Genetic information
Genetic testing
How you find out about variants
CLDN18 genetic testing looks for variants in the CLDN18 gene using a blood sample, saliva, or a cheek swab. A lab reads the gene’s DNA sequence and compares it with the usual sequence to identify a relevant variant, which can help clarify whether a person has a gene related condition or carries a familial change.
When should I consider getting a genetic test?
There is not yet a broadly established reason for most people to have CLDN18 genetic testing based on this gene alone. Testing decisions are usually made with a doctor or genetic counselor, using your personal health history, family history, and any other findings that may point to a specific inherited condition.
A genetic result is only one part of your health story
A genetic result can be helpful, but what it can tell you varies with the condition and the kind of variant involved. Over time, the body is shaped by many factors, including lifestyle, environment, age, and medical history. In some conditions, particularly those affected by many genes, genetic information offers context rather than certainty and makes the most sense when viewed with other parts of care. In other situations, a genetic result can give a clear answer. For topics like medication response, it can also help put personal experiences in context.
Pharmacogenetics
How variants shape your response to medicine
Genetic variation can affect how your body responds to medicines, including how well a treatment works and how likely side effects may be. Small differences in genes that help absorb, break down, move, or respond to a drug can change how much medicine reaches its target. This is common and helps explain why the same medication may work well for one person, do less for another, or make someone more sensitive to its effects.
What is Pharmacogenetics?
Pharmacogenetics examines how differences in genes can affect the way a person responds to medications. It studies the relationship between genes and drugs to better understand why the same treatment can work differently from one person to another. For many medicines, genes influence how the body processes a drug or how strong its effects are. This information can support more informed, more individualized treatment decisions. You can read more about this topic in the LearnHub.
Drugs influenced by the CLDN18 gene
When should I seek medical advice?
There is not yet a broadly confirmed role for this gene in predicting how most medicines will work, so general medication questions are best discussed with your doctor. CLDN18 is mainly relevant in some stomach and nearby esophagus cancers, where a tumor form called CLDN18.2 can help guide certain targeted treatment choices with a cancer specialist.
History
CLDN18 entered medical research through work on the claudin family, a group of genes identified in the late 1990s as key parts of the body’s tissue barriers. In recent decades, awareness of this gene’s role has grown, especially in stomach and lung research. Scientists later recognized that different forms of the CLDN18 gene are active in different tissues, which helped explain why it kept appearing in studies of gastric disease. Building on this early work, scientists uncovered more about the gene when CLDN18 changes and CLDN18-ARHGAP fusions were linked to some stomach cancers. Its clinical profile expanded further when CLDN18.2 became a treatment target in advanced gastric and gastroesophageal cancers. These milestones made CLDN18 part of a broader shift toward more precise, biomarker-based cancer care.