Psoriatic arthritis (PsA) is a type of arthritis that affects some people with psoriasis, an autoimmune skin condition that causes itchy and scaly skin. This type of arthritis causes swollen, stiff, or painful joints and tends to get worse over time.

Researchers aren’t completely sure why some people with psoriasis develop psoriatic arthritis. Many people who develop it have close relatives also affected, which suggests a strong genetic component.

In people with psoriatic arthritis, immune cells attack healthy cells in the joints and cause inflammation. Researchers have identified some genes that may play a role in the development of this immune reaction. Multiple genes seem to be involved.

Keep reading to learn more about the connection between psoriatic arthritis and your genetics.

About 20 to 30 percent of people with psoriasis develop psoriatic arthritis. On average, psoriatic arthritis symptoms develop 10 years after skin symptoms. Skin and arthritis symptoms develop at the same time in about 15 percent of people.

Researchers are still trying to figure out why some people with psoriasis develop psoriatic arthritis, and others don’t. It’s likely that a complex combination of genetic and environmental factors contributes.

About 33 to 50 percent of people with psoriatic arthritis have at least one sibling or parent who also has it. Some of the genes associated with the development of psoriatic arthritis are in the human leukocyte antigens (HLA) region of chromosome six. This region is associated with immune function.

Some non-HLA genes associated with immune function have also been identified as potential contributors.

In a 2021 review of studies, researchers examined all the available evidence to assess whether any genetic markers are consistently associated with psoriatic arthritis.

They didn’t find a strong level of evidence that any individual genetic markers were associated with psoriatic arthritis. Among genetic markers investigated in multiple studies, they found a moderate amount of evidence that six genetic markers were positively associated with the presence of psoriatic arthritis in people with psoriasis. They included:

  • two variations of the HLA-B27 gene
  • one variation of the HLA-B38 gene
  • one variation of the HLA-B39 gene
  • presence of HLA-B*12
  • presence of polymorphism rs1800925 in the IL13 gene

About 33 to 50 percent of people with psoriatic arthritis have first-degree relatives with psoriasis. A first-degree relative is a family member who shares half of your DNA, which would be a biological parent or full sibling.

It’s estimated that about 80 percent of the heritability of psoriatic arthritis comes from your genetics.

The vast majority of people who develop psoriatic arthritis have already been diagnosed with psoriasis.

Psoriatic arthritis tends to develop 7 to 10 years after skin symptoms, according to the National Institute of Arthritis and Musculoskeletal and Skin Diseases. You can develop it at any age, but it becomes more common as you get older and seems to peak slightly before age 60.

In the 2021 review, researchers found a moderate association between psoriatic arthritis and sores in the buttock fold and nail pitting. They found conflicting evidence of an association with obesity or psoriasis severity.

In another 2021 study, researchers compared potential risk factors for psoriatic arthritis, psoriasis, rheumatoid arthritis, and ankylosing spondylitis. They found that psoriatic arthritis:

  • was associated with obesity, pharyngitis, and skin infections
  • and psoriasis were associated with obesity and moderate alcohol intake
  • and rheumatoid arthritis were associated with gout
  • and ankylosing spondylosis was associated with uveitis, swelling of the middle layer of your eye

In a 2020 study, researchers found genetic testing had a marginal ability to predict the future development of psoriatic arthritis among people with psoriasis.

The development of psoriatic arthritis is likely caused by a combination of genes. Some genes like HLA-B27 have been found to be moderately associated with PsA, but even if you have this gene, you might not develop psoriatic arthritis.

It’s likely that genetic testing may become more accurate as researchers improve their understanding of the genetics behind psoriatic arthritis.

A combination of tests is necessary to diagnose psoriatic arthritis. If your doctor thinks you might have it, they will refer you to a joint specialist called a rheumatologist.

A rheumatologist will consider your symptoms, look for skin changes typical of psoriasis, and look for a pattern of arthritis common with psoriatic arthritis.

They may order imaging tests to search for joint damage indicative of psoriatic arthritis. Imagining tests might include:

A rheumatologist may also order blood tests to rule out other types of arthritic conditions that may cause similar symptoms, such as:

Sometimes, a small skin sample called a biopsy is needed for lab analysis to confirm that you have psoriasis.

Symptoms of psoriatic arthritis tend to get worse over time. In the early stages, they may include:

The U.K.’s National Health Service recommends getting medical advice if you have persistent pain, swelling, or stiffness in your joints even if you don’t have psoriasis.

If you do have psoriasis, it’s a good idea to get a checkup once a year to let a doctor know if you have any joint problems.

Researchers are still trying to figure out why some people with psoriasis develop psoriatic arthritis. About a third to half of people with a sibling or parent with psoriatic arthritis go on to develop psoriatic arthritis themselves.

No single gene is associated with the development of psoriatic arthritis. Many genes are thought to contribute, but more research is needed to understand the complex interaction between these genes.

If you experience any symptoms of psoriatic arthritis, it’s a good idea to see a doctor for a proper diagnosis and treatment.