The HDC gene gives the body instructions to make histamine, a chemical messenger involved in wakefulness, stomach acid production, and some immune responses. If it does not work properly, histamine levels can be lower than usual, which may affect these body functions. This gene can play a role in how your body responds to signals between nerve cells and in the gut. Rare variants in the HDC gene have been linked to tic disorders in some families, but most people with tics do not have a condition caused by the HDC gene.
What is a gene?
A gene is a stretch of DNA that carries instructions your cells use to make molecules or regulate processes in the body. Some genes hold the directions for making proteins, which are the working parts of cells. Other genes mainly help determine when, where, and how strongly certain processes take place. Together, genes affect how the body develops and works, and they can influence how you respond to food, stress, or medications. To explore this topic in more detail, you can learn more in the LearnHub.
Overview
HDCGene function
What if the gene works
The HDC gene helps your body make histamine, a chemical messenger. Histamine supports stomach acid release, immune responses, and some brain signaling.
Risk
What if the gene does not work
Milder to more severe variants in the HDC gene can lower or shut down the body's ability to make histamine. This can disrupt histamine signaling between nerve cells, immune cells, and stomach cells.
Treatment
What does that mean for your treatment
No treatment or management approach is currently established specifically for people with a pathogenic or loss-of-function variant in the HDC gene. The HDC gene is still being studied in histamine-related brain and immune pathways, but this has not yet changed routine drug choices.
Gene function
What if the gene works
The HDC gene helps your body make histamine, a natural chemical messenger. Histamine supports everyday processes in the stomach, immune system, and brain. Understanding what the HDC gene does helps explain how your body handles digestion, alertness, and routine cell communication.
The HDC gene gives cells instructions to turn histidine, a building block from protein, into histamine. This is the main step that supplies histamine for several body systems.
In the stomach, histamine helps signal cells to release acid for digestion. This supports the breakdown of food and helps your body absorb some nutrients.
In the brain, histamine acts as a messenger between nerve cells. It helps support wakefulness, attention, and other steady daily brain functions.
Histamine also helps immune cells send local signals during routine body responses. This supports changes in nearby blood vessels and helps coordinate early tissue reactions.
What is a variant?
A genetic variant is a minor difference in the DNA sequence within a gene. Variants are common and help explain normal differences among people, such as appearance, metabolism, or the way the body responds to environmental influences. Many have no noticeable effect and are simply part of natural genetic variation. Sometimes, though, a variant changes how a gene works more substantially and can contribute to or cause a genetic condition.
Genetic variants
What if the gene does not work
Variants in the HDC gene can alter how the cell makes or handles the histidine decarboxylase enzyme, which is why people often look for how HDC gene variants affect histamine production. Milder variants may leave some enzyme activity, while more severe variants can disrupt folding, shorten the protein, or stop it from being made at all. In cells, this often means reduced enzyme stability or lower catalytic activity, with less conversion of histidine into histamine.
How variants are linked to conditions
Research on how variants in the HDC gene are linked to conditions is still developing, and this gene does not yet have a broadly confirmed connection to one specific health condition. If you have a confirmed HDC-related diagnosis, care is best guided by your doctor or genetic counselor rather than general summaries online.
A variant is not necessarily a diagnosis
Genetic variants are a common and expected feature of human biology across the general population. Most do not directly affect health and instead reflect normal human diversity. For many genes, having a variant associated with a condition points to a possible link rather than a certain diagnosis, particularly when several genes and environmental influences play a role. In some situations, though, 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 risks related to the HDC gene. In most situations, any effects of HDC are likely shaped by many other genes and by everyday factors such as overall health and environment. Anyone concerned about personal risk can talk with a doctor or genetic counselor.
Inheritance of HDC variants
There is not yet a broadly confirmed, single disease inheritance pattern for HDC that applies across clinical use, so how HDC gene variants are inherited in relation to a specific condition is still being clarified. The HDC gene is located on chromosome 15, which is an autosome, so each person inherits one copy from each parent. In general, that means an HDC variant can be passed from either mother or father to a child.
What does my HDC result mean for my family?
There is not yet a broadly confirmed inheritance pattern tied to a specific condition for HDC, and different changes in this gene may not all have the same meaning for families. If you have a specific HDC result, a doctor or genetic counselor can explain whether it may matter for close relatives such as parents, siblings, or children.
Genetic information
Genetic testing
How you find out about variants
To look for changes in the HDC gene, a lab uses genetic testing on a blood, saliva, or cheek swab sample and reads the gene’s DNA code for variants. Genetic testing for HDC variants can show whether you carry a specific variant, and the result is interpreted in the context of your personal and family history.
When should I consider getting a genetic test?
There isn't yet a broadly established, HDC-specific clinical reason for testing. Testing decisions are usually made with a doctor or genetic counselor based on symptoms, personal history, and family history.
A genetic result is only one part of your health story
A genetic result can provide valuable insight, but how much it can tell you varies based on the condition and the kind of variant involved. Many other factors, including lifestyle, environment, age, and medical history, also influence how the body works over time. In some conditions, especially those shaped by many genes, genetic information provides context rather than certainty and is best understood together with other parts of care. In other situations, a genetic result can offer a clear answer. In areas such as medication response, genetic results can also help place personal experiences in perspective.
Pharmacogenetics
How variants shape your response to medicine
Genetic variation can affect how people respond to medicines. This helps explain why the same treatment may work well for one person, have less effect in another, or cause more side effects in someone else. Part of the reason is that inherited differences can change how the body breaks down, moves, or responds to a drug, and this kind of variation is common.
What is Pharmacogenetics?
Pharmacogenetics examines the way genetic differences affect a person’s response to medications. By studying links between genes and drugs, it helps explain why the same treatment can work differently in different people. With many medicines, genes can influence either how powerfully a drug works or how the body handles it. This information can support treatment decisions that are more informed and more individualized. More detail on this topic is available in the LearnHub.
Drugs influenced by the HDC gene
When should I seek medical advice?
There is not yet a broadly confirmed role for this gene in predicting how people respond to medicines. Questions about symptoms, side effects, allergies, or any treatment plan are best discussed with your doctor or pharmacist.
History
Histamine was identified in the early 1900s, and researchers later traced its production to an enzyme that led to the discovery of the HDC gene. The human HDC gene was isolated and described in the late 20th century as molecular genetics made it possible to connect older biochemical findings with specific genes. From these first observations, research expanded steadily. Interest in the HDC gene grew further when rare inherited variants were reported in a family with Tourette syndrome, which brought this gene into neuropsychiatric research as well as allergy and stomach acid studies. Over time, scientists’ understanding of the HDC gene’s place in human health has become more precise.