Are Ulcers Hereditary? The Role of Genetics and H. Pylori

Peptic ulcers run in families, but they are not hereditary in the way most people imagine. There is no single “ulcer gene” passed down from parent to child. Instead, genetics account for somewhere between a third and two-thirds of a person’s susceptibility, depending on which study you look at, with the bacterium Helicobacter pylori acting as the dominant environmental trigger. The interplay between your genes and this particular infection is where the real story lives, and it is considerably more interesting than a simple yes-or-no answer about inheritance.

What Twin Studies Reveal

The strongest evidence for a genetic contribution to peptic ulcer disease comes from twin research. A large nationwide study of Danish twins found that identical twins were concordant for ulcers at a rate of about 24%, compared with roughly 15% for fraternal twins. Using statistical modeling, the researchers estimated that about 39% of the liability to peptic ulcer disease was explained by genetic factors, with the remaining 61% attributable to individual environmental factors like diet, smoking, stress, and infection.¹ That 39% figure is meaningful, but notice what it tells you: environment still matters more than genes.

A separate study of Swedish twins, which included twins reared apart, pushed the heritability estimate considerably higher. The correlation for identical twins raised in different households was 0.67, suggesting that roughly 62% of the variation in ulcer risk could be chalked up to genetics.² The gap between the two estimates (39% versus 62%) probably reflects differences in study design, populations, and how H. pylori exposure was accounted for. What both studies agree on is that genetic factors are real and substantial, but they never tell the whole story.

H. Pylori Is Still the Main Event

For all the talk of genetics, the single most important cause of peptic ulcers remains H. pylori infection. This spiral-shaped bacterium colonizes the stomach lining, triggers chronic inflammation, and can erode the mucus barrier that protects your stomach and duodenum from their own acid. Most ulcers that are not caused by painkillers like ibuprofen or aspirin trace back to this organism.

Here is where family patterns get confusing. H. pylori spreads readily within households, mainly through oral-oral or fecal-oral contact. A study of community households in Lanzhou found significant clustering of H. pylori infection within families.³ So when you see multiple family members with ulcers, the obvious question is whether they share genes for ulcer susceptibility or whether they simply shared the same bacterium across the dinner table. The answer, inconveniently, is often both.

Research on transmission patterns has shown that living together matters more than blood relatedness. In one study of a large extended family, the similarity of H. pylori strains correlated with household membership, not with how closely people were related genetically. Transmission happened between people who shared a home, regardless of kinship.⁴ This is a critical point: a family history of ulcers may reflect shared infection rather than shared DNA. If your mother and grandmother both had ulcers, you might have inherited some genetic vulnerability, but you also might have picked up the same bug in childhood.

Not All H. Pylori Strains Are Equal

The genetics of the bacterium itself matter too. H. pylori is genetically diverse, and certain strains are far more dangerous than others. Two virulence genes in particular, known as cagA and vacA, dramatically affect disease severity. When both are present in their most aggressive forms, the odds of developing a peptic ulcer rise sharply. One analysis found that the most virulent vacA variant increased the odds of peptic ulceration more than four-fold, while cagA roughly doubled the risk.⁵

This means that two people can both be infected with H. pylori and have very different outcomes, not because of their own genes, but because of the bacterium’s genes. Whether you picked up an aggressive strain or a relatively mild one depends on who transmitted it to you and where in the world you live.

Blood Type and the Ulcer Connection

One of the oldest known genetic links to ulcers involves something most people already know about themselves: blood type. People with blood type O have a modestly higher risk of developing gastric and duodenal ulcers. A large Japanese cohort study found that women with blood type O had about an 18% higher risk of ulcers compared with women of other blood types.⁶

The reason appears to involve how H. pylori attaches to stomach cells. The bacterium binds more easily to the surface molecules on the stomach lining of people with type O blood, which leads to denser colonization and a stronger inflammatory response.⁷ The effect is real but modest. Having blood type O does not mean you will get an ulcer; it just shifts the odds slightly in the wrong direction if you are also infected with H. pylori. Without the infection, blood type alone does very little.

Immune Genes That Dial Inflammation Up or Down

When H. pylori sets up shop in your stomach, your immune system fights back by producing inflammatory signaling molecules called cytokines. How aggressively your body mounts this response is partly determined by variations in the genes that control cytokine production. Some people carry gene variants that crank up inflammation in response to H. pylori, while others have variants that keep the response more muted.⁸

A meta-analysis confirmed that certain variants in the IL-8 gene were associated with a higher risk of H. pylori-related peptic ulcer disease.⁹ Paradoxically, a stronger inflammatory response does not necessarily clear the infection better. Instead, it can damage the stomach lining more severely, making an ulcer more likely even though the body is “trying harder” to fight the bug. This is a case where your genes do not cause ulcers directly but instead shape how much collateral damage the infection inflicts.

When Human and Bacterial Ancestry Collide

One of the more fascinating findings in ulcer genetics comes from research on coevolution. Humans and H. pylori have been traveling together for at least 60,000 years, and over that time, local populations and their local strains have adapted to each other. A study in Colombia demonstrated this strikingly. In one region, people of predominantly African ancestry carried H. pylori strains of African origin, and gastric disease was relatively mild. In another region, people with substantial Amerindian ancestry were infected with those same African-origin strains, and the disease was far more severe. The mismatch between host ancestry and bacterial ancestry completely accounted for the difference in disease severity between the two populations.¹⁰

The implication is striking: when people migrate and encounter H. pylori strains they did not coevolve with, disease risk can jump. This is a form of genetic influence on ulcer risk that has nothing to do with individual gene variants and everything to do with the broad evolutionary history of a population and its parasites. It may help explain why some ethnic groups experience higher rates of gastric disease even after accounting for known risk factors.

Rare Genetic Conditions That Directly Cause Ulcers

While most ulcers arise from the complex interplay of common gene variants and H. pylori, a small number of genetic conditions cause ulcers more directly. These are uncommon but worth knowing about, especially if ulcers show up in unusual patterns within a family.

One is an inherited tendency toward elevated serum pepsinogen I, a precursor to the stomach enzyme pepsin. In certain families, elevated pepsinogen I segregates as a classic inherited trait, and people who carry it tend to have excessive acid production and a markedly increased risk of duodenal ulcers. In one study, ten of eleven family members who had clinical ulcer disease also had this elevated marker.¹¹ This represents a genuine hereditary form of ulcer disease: a single gene variant leads to overproduction of acid, which leads to ulcers, sometimes even without H. pylori involvement.¹²

Another rare condition is Zollinger-Ellison syndrome, in which tumors called gastrinomas produce massive amounts of the hormone gastrin, driving the stomach to secrete dangerously high levels of acid. Zollinger-Ellison syndrome can occur on its own, or it can appear as part of a hereditary syndrome called multiple endocrine neoplasia type 1 (MEN1), caused by mutations in the MEN1 gene.¹³ People with MEN1-related Zollinger-Ellison syndrome often develop ulcers at a young age, and the condition runs unmistakably through families.

The Modern Genomic Picture

Advances in genomic technology have allowed researchers to move beyond twin studies and individual candidate genes to scan the entire genome for variants linked to peptic ulcer disease. These large-scale studies paint a picture of a trait influenced by many genetic variants, each contributing a small amount of risk.

A genome-wide study using UK Biobank data identified eight independent genetic variants reaching statistical significance for peptic ulcer disease, some of which overlapped with genes involved in other digestive conditions like gastroesophageal reflux and inflammatory bowel disease.¹⁴ A larger cross-ancestry analysis combining Japanese and European data, with over 52,000 cases and 905,000 controls, uncovered 25 additional risk loci that had not been seen before, many of them consistent across ancestries.¹⁵ Some of these variants sit near genes involved in stomach acid secretion, mucus production, and immune regulation, which makes biological sense.

What these studies tell us is that ulcer susceptibility is polygenic. There is no single gene to test for. Instead, hundreds or possibly thousands of small-effect variants add up, and their cumulative effect interacts with whether you happen to encounter H. pylori, take NSAIDs regularly, smoke, or drink heavily. Polygenic risk scores for ulcers are still in the research phase and are not used clinically.

How Your Genes Affect Ulcer Treatment

Even if you do develop an ulcer, your genetics can shape how well treatment works. The standard approach to H. pylori eradication involves a proton pump inhibitor (PPI) combined with antibiotics. PPIs are broken down in the liver by an enzyme encoded by the gene CYP2C19, and people vary considerably in how active their version of this enzyme is.¹⁶

People who metabolize PPIs quickly (sometimes called extensive metabolizers) break down the drug before it can fully suppress stomach acid, which reduces its effectiveness. In one study, H. pylori eradication rates were about 73% in people who metabolized PPIs rapidly, compared with roughly 98% in people who metabolized them slowly.¹⁷ That is a substantial gap. Nearly all of the treatment failures in that study occurred in people with the rapid-metabolizer version of the gene. Genotype-guided dosing of PPIs, where people who metabolize the drug quickly receive a higher dose, is an active area of research and is already being explored in clinical practice.

CYP2C19 variants are not distributed evenly across populations. The slow-metabolizer version is more common in East Asian populations than in European ones, which partly explains why standard-dose PPI triple therapy has historically shown higher eradication rates in some Asian studies than in Western ones. Your ancestry can indirectly affect your treatment outcome through this pharmacogenetic pathway.

NSAIDs and the Genetics of Gut Bleeding

Anti-inflammatory painkillers like ibuprofen, naproxen, and diclofenac are the second most common cause of peptic ulcers after H. pylori. Many of these drugs are metabolized by another liver enzyme, CYP2C9, and researchers have wondered whether people who carry slow-metabolizer versions of this gene (and therefore clear the drugs more slowly) might face a higher risk of ulcer-related bleeding.

The evidence here is genuinely mixed. One study found evidence for a genetic susceptibility to NSAID-related gastroduodenal bleeding in people taking CYP2C9-metabolized painkillers during short-term treatment.¹⁸ But other studies have failed to confirm the link. One found that CYP2C9 genotype was not a significant risk factor for serious NSAID-related ulcers.¹⁹ Another reached a similar negative conclusion.²⁰ For now, CYP2C9 testing is not recommended as a way to predict who will develop NSAID-related ulcers, though the question has not been fully settled.

Idiopathic Ulcers and the Remaining Unknowns

A small but growing fraction of peptic ulcers occur in people who test negative for H. pylori and do not use NSAIDs. These so-called idiopathic ulcers are not well understood, but genetic predisposition is considered one plausible contributing factor, alongside older age, smoking, chronic conditions, and vascular insufficiency affecting the stomach lining.²¹

Emerging research has also begun to look beyond H. pylori to the broader community of microbes living in the gut. A Mendelian randomization study suggested that certain bacterial groups in the gut microbiome may increase or decrease the risk of gastric and duodenal ulcers independently of H. pylori. Several members of the Clostridiaceae family, for instance, were associated with increased ulcer risk, while certain Lachnospiraceae members appeared protective.²² The composition of your gut microbiome is shaped by both your genes and your environment, adding yet another layer to the hereditary puzzle.

H. Pylori and Epigenetic Changes

There is one more way that infection and genetics intertwine that does not fit neatly into either category. H. pylori infection can alter how your genes are read without changing the genes themselves. The bacterium triggers chemical modifications to DNA in stomach cells, silencing certain protective genes and potentially setting the stage for more severe disease or even cancer over decades of chronic infection.²³ These epigenetic changes are not inherited in the traditional sense, but they represent a pathway through which an environmental exposure (the infection) produces lasting changes in gene activity that affect disease risk. It is a reminder that the boundary between “genetic” and “environmental” causes is blurrier than textbook categories suggest.

Whether some epigenetic marks caused by H. pylori could be passed to offspring is an open question in gastric research. Most evidence points to these changes being acquired during an individual’s lifetime rather than transmitted across generations, but the field is still young. What is clear is that treating and eradicating H. pylori reverses some of these modifications, which is one more argument for testing and treating the infection early rather than assuming ulcers are simply a family destiny you cannot escape.