Psoriatic arthritis (PsA) is a type of arthritis that often affects people who have psoriasis. Researchers have identified genetic markers for both psoriasis and PsA.

PsA is not always hereditary, but some people may inherit a predisposition to developing it. There is some overlap in the genetic predisposition to psoriasis, PsA, and a type of arthritis called ankylosing spondylitis.

About 30% of people with psoriasis develop PsA, and 33–50% of people with PsA have at least one first degree relative with psoriasis or PsA. Most people who have both conditions develop symptoms of psoriasis first, with symptoms of arthritis occurring about 10 years later, on average. However, in about 15% of cases, the symptoms appear at the same time or in the other order.

Experts believe that PsA likely occurs due to a combination of genetic and environmental factors.

A 2020 study suggests that genes that predispose a person to develop PsA can pass from parents to their children. For example, some human leukocyte antigen (HLA) genes, which are related to immune function, may be associated with PsA. Both psoriasis and PsA are autoimmune diseases.

The genetics of PsA are complicated. Some genes associated with psoriasis are not associated with PsA and vice versa. However, researchers have found more than 20 genetic variants that may be linked to PsA.

A 2021 review of studies found no strong evidence of genetic markers that can predict whether someone with psoriasis might develop PsA. However, the researchers did find moderate evidence of six markers associated with PsA. These are:

  • HLA-B*27-C*01
  • HLA-B*27-C*02
  • HLA-B*38-C*12
  • HLA-B*39:01-C*12
  • HLA-B*27
  • single nucleotide polymorphism (SNP) rs1800925 in the IL13 gene

The researchers placed high importance on finding more genetic markers that could help with early detection.

A 2022 research article outlines a new predictive model that might help assess the risk of PsA in people with psoriasis. A high risk of PsA is associated with:

  • age at onset being 40 years or older
  • duration of psoriasis longer than 180 months
  • nail involvement

Genetic testing looks for variants in DNA. These tests can use blood or saliva samples. Genetic testing can help determine whether someone has an increased risk of developing certain conditions. In some cases, this can help with lowering their risk or determining the best treatment.

In cases of psoriasis, a 2020 study suggests that genetic testing may have only a marginal effect in predicting whether a person is likely to develop PsA.

Dr. Suzanne Friedler is a dermatologist at Advanced Dermatology in New York. She told Medical News Today that there are genetic markers and familial hereditary patterns that make someone more likely to develop psoriasis and PsA.

“We don’t have lab tests for these things right now, but it can be helpful to look at your family history. If PsA runs in the family, then look at your own health. People who are overweight, smoke, have poor cardiovascular health, or diabetes have a higher incidence of PsA,” said Dr. Friedler.

Dr. Friedler urges those with a family history of psoriasis and PsA to adopt a healthy lifestyle and be aware of early warning signs, such as joint stiffness.

Dr. Orrin Troum is a rheumatologist at Providence Saint John’s Health Center in Santa Monica, CA. He told MNT that genetics is just one aspect of the risk of developing PsA.

“The underlying causes are not exactly clear. There are environmental factors and immunological mechanisms in play, not just genetics. There are things that seem to trigger the immune system and inflammatory events throughout the immune system, and other factors that are not so well-understood,” said Dr. Troum.

Dr. Troum does not recommend genetic testing for PsA, as it may cause unnecessary worry. Having one of the gene variants associated with PsA does not necessarily mean that the individual will develop it.

However, he noted that family history is helpful in making the diagnosis. He also stressed the importance of getting a good physical examination of the skin when joint problems occur.

Genetic makeup may play a role in the severity of psoriasis and arthritis. However, Dr. Troum explained that genes are more likely to influence whether a person has PsA than how it progresses.

More important than genetics, said Dr. Friedler, is having healthy habits. “Things that cause inflammation make psoriasis and PsA worse,” she said. Examples include eating a lot of sugar, smoking, excessive alcohol consumption, and high levels of stress.

If an individual already has psoriasis and wants to protect their joints, Dr. Friedler recommends consulting a doctor. “There are medications that protect joints and slow down progression.”

It may be that specific gene variants influence the response to a particular treatment. However, research in this area is preliminary.

At this point, genetic testing is not helpful in diagnosing or treating PsA, said Dr. Friedler.

“We know we can protect joints with biologics. These are medicines that target certain points in the immune system. They decrease inflammation and have a protective effect on joints.”

Dr. Friedler explained that psoriasis manifests on the skin, and PsA manifests in the joints. “But when you have less inflammation, you have less of these reactive conditions. So, take care of yourself. Lower stress, get good sleep, meditate. Healthy habits can certainly affect disease progression.”

“We are treating PsA with revolutionary medicines,” added Dr. Troum. “They have improved over the last 20 years, and there are more coming down the line.”

PsA is a type of arthritis that occurs in people with psoriasis. More than 20 gene variants are associated with PsA. Researchers have linked other variants to psoriasis or PsA, but not both.

It is likely that a combination of genetic and environmental factors is involved.

Currently, no genetic test can reliably predict who might get PsA, how it will progress, or the best treatment. On the other hand, it appears that certain genes may predispose someone to develop PsA, so family history is an important piece of the puzzle.

Experts note that medications are available that can effectively manage the symptoms and slow disease progression.