The CLDN19 gene helps form tight seals between cells in the kidneys and eyes, which lets the body handle minerals like magnesium and calcium in a controlled way. If it does not work properly, a person may lose too much magnesium in urine, pass extra calcium, develop kidney stones or calcium buildup in the kidneys, and have vision problems. This gene plays an important role in keeping kidney tissue and parts of the eye working normally. Pathogenic variants in the CLDN19 gene are linked to an inherited condition called familial hypomagnesemia with hypercalciuria and nephrocalcinosis.
What is a gene?
Genes are pieces of DNA that carry instructions your cells use to make molecules or direct activities in the body. Some genes provide the code for proteins, which are the active components inside cells. Others mainly regulate when specific processes happen, where they happen, and how active they are. In combination, genes affect how the 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 find more in the LearnHub.
Overview
CLDN19Gene function
What if the gene works
The CLDN19 gene helps make tight junctions, which are seals between neighboring cells. In the kidneys and retina, this supports controlled salt movement and helps tissues work properly.
Risk
What if the gene does not work
Variants in the CLDN19 gene can cause low magnesium, high urine calcium, calcium buildup in the kidneys, and eye problems. Milder or more severe variants may influence when symptoms appear and how much the kidneys and eyes are affected.
Treatment
What does that mean for your treatment
No CLDN19-specific treatment is currently established. Care is supportive and may include magnesium supplements, steps to lower urine calcium such as thiazide diuretics, kidney follow-up, and eye care, but drug choices are not guided by the CLDN19 gene itself.
Conditions associated with CLDN19
Gene function
What if the gene works
Many cell layers in your body need close, well-controlled connections so fluids and minerals move in the right direction. The CLDN19 gene helps build these seal-like links, called tight junctions, between neighboring cells. When it works properly, these barriers stay organized and selective.
The CLDN19 gene helps neighboring cells lock together at tight junctions, which are seal-like connections between cells. This creates a neat barrier across a layer of cells.
Its protein helps control which salts and other small molecules can pass through the space between cells. This keeps movement more measured instead of letting substances pass freely.
By supporting tight junctions, the CLDN19 gene helps cells keep their proper top and bottom sides, called polarity (their built-in orientation). This is part of how the CLDN19 gene helps kidney and eye cell layers handle fluid and salt movement.
What is a variant?
A genetic variant is a small difference in the DNA sequence of a gene. These changes are common and help shape normal human diversity, including differences in appearance, metabolism, or the way the body responds to environmental influences. Many variants do not have any noticeable effect and simply represent natural genetic variation. In some situations, though, a variant can change 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 CLDN19 gene can change the claudin-19 protein so it folds poorly, becomes unstable, or does not reach cell junctions where it needs to work. How CLDN19 gene variants affect protein function depends on the change: some leave partial activity, while more severe variants can cause little or no working protein. This weaker cell barrier can disrupt kidney mineral handling and sometimes affect the eyes, with more disruptive variants often linked to earlier kidney and eye features.
How variants are linked to conditions
Variants in the CLDN19 gene are most strongly linked to familial hypomagnesemia with hypercalciuria and nephrocalcinosis, a rare inherited kidney condition. People with two disease-causing variants typically have low blood magnesium, high calcium loss in the urine, kidney calcification or stones, and kidney disease that can worsen over time. Many also have eye findings such as strong nearsightedness, involuntary eye movements, or changes in the retina.
A variant is not necessarily a diagnosis
Genetic variants are a routine part of human biology and are widely found in the general population. Most do not have a direct effect on health and simply contribute to natural human variation. For many genes, having a variant associated with a condition suggests a possible link rather than a definite diagnosis, especially when several genes and environmental factors also play a part. In some situations, though, a single well characterized variant in a particular gene is enough to confirm a diagnosis.
Are there things that can increase or change my risk?
For CLDN19, risk is mainly set by inheritance: the condition usually happens when a child receives harmful changes in both copies of the gene, so having carrier parents or an affected brother or sister raises the chance. There is not enough evidence to say lifestyle changes lower the chance of having this genetic condition, but early kidney and eye checks can help find problems sooner.
Inheritance of CLDN19 variants
CLDN19-related conditions follow an autosomal recessive inheritance pattern. This means a child usually inherits one CLDN19 variant from each parent, and the parents are often healthy carriers. When both parents carry a variant in the CLDN19 gene, each pregnancy has a 25% chance of resulting in an affected child, a 50% chance of a carrier child, and a 25% chance of a child with no familial variant. In practical terms, the CLDN19 inheritance pattern can affect brothers and sisters equally, and mothers and fathers can pass the variant on in the same way.
What does my CLDN19 result mean for my family?
Changes in the CLDN19 gene are linked to a rare kidney and eye condition that usually runs in families in a recessive pattern. For family members, this often means brothers and sisters could also be affected or could carry the same gene change even if they feel well. Parents are often healthy carriers, and other relatives may also carry the change.
Genetic information
Genetic testing
How you find out about variants
To find out whether you carry a variant in the CLDN19 gene, CLDN19 genetic testing uses a blood or saliva sample. A lab reads the gene's DNA sequence to look for variants, which can help confirm a diagnosis or show whether a family member carries the same inherited change.
When should I consider getting a genetic test?
Consider CLDN19 genetic testing if you or your child has very low magnesium, high calcium in the urine, kidney stones or calcium buildup in the kidneys, especially along with vision problems. Testing can also help when these problems run in the family or start early in life.
A genetic result is only one part of your health story
A genetic result can be informative, but how much it reveals depends on the condition and the type of variant involved. Many other factors, including lifestyle, environment, age, and medical history, also shape how the body works over time. In some conditions, especially those influenced by many genes, genetic information offers context rather than certainty and is best considered alongside other parts of care. In other situations, a genetic result may give a clear answer. In areas like medication response, genetic results can also help put individual experiences into context.
Pharmacogenetics
How variants shape your response to medicine
Genetic variation can affect how your body handles some medicines, so the same treatment may work differently from one person to another. Small inherited differences can change how a medicine is broken down, how it moves through the body, or how strongly the body responds to it. These differences are common and can influence how well a treatment works or how sensitive someone is to side effects.
What is Pharmacogenetics?
Pharmacogenetics looks at how genetic differences can shape a person’s response to medication. It examines links between genes and drugs to help explain why the same treatment can work differently from one person to another. For many medicines, genes influence either how strongly a drug works or how the body processes it. This information can support more informed, individualized treatment decisions. If you want to learn more about this topic, you can explore it further in the LearnHub.
Drugs influenced by the CLDN19 gene
When should I seek medical advice?
There is not yet a broadly confirmed role for this gene in how people respond to medicines. General health concerns or questions about treatments and side effects are best discussed with your doctor.