IBD patients facing greater disease risk for forms of AS: Study

But those with SpA aren't at higher risk of inflammatory bowel disease

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by Lindsey Shapiro |

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People with inflammatory bowel disease (IBD) are at significantly higher risk for various forms of spondyloarthritis (SpA), including ankylosing spondylitis (AS), a study found.

But the reverse wasn’t true: Having SpA was not linked to an increased risk of developing IBD, according to the new analysis, which used genetic data. The researchers had aimed to identify relationships between the two conditions, which often co-exist among patients.

The study “lays the groundwork for future investment in validation intervention trials and exploration of novel therapeutic targets,” the team wrote.

The results, the researchers added, indicate that “preventing SpA in individuals with IBD is needed” in clinical settings.

Titled “Mendelian randomization analysis reveals causal associations of inflammatory bowel disease with Spondylarthritis,” the study was published in Gene.

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Genetic analysis identifies link between AS, IBD

SpA encompasses a group of chronic inflammatory diseases affecting the joints. It can include axial forms, which mainly affect the spine, and peripheral types that predominately affect joints outside of the spine. AS is a common axial type of SpA, while peripheral types include psoriatic arthritis and reactive arthritis.

IBD refers to a group of inflammatory gastrointestinal conditions such as Crohn’s disease and ulcerative colitis.

Beyond the joints, inflammation in the gastrointestinal tract and associated bowel symptoms are common in SpA. In people with IBD, joint symptoms are the most common symptom outside of the intestinal tract.

While SpA and IBD are known to overlap, and studies have shown that they may have a shared genetic basis, no causal relationship between the two diseases has been established.

Now, a team of researchers studied the relationship using a type of analysis called mendelian randomization or MR. It essentially uses genetic signatures of a clinical feature — IBD here, for example — to identify its causal relationship with a later clinical outcome, such as SpA.

Data for MR analyses come from existing genome-wide association studies, which collect clinical and genetic information from several thousand people.

The study’s IBD-related genetic data came from the International IBD Genetics Consortium, and data associated with SpA were from the FinnGen Consortium. Altogether, the data came from more than 31,000 people diagnosed with IBD, more than 7,000 with various forms of SpA, and many more matched controls from the general population. All were of European descent.

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AS disease risk about 28% higher for IBD patients

The analysis identified a causal relationship between IBD and AS, with  the presence of the gastrointestinal disorder increasing the risk of AS by about 28%.

Crohn’s disease increased the risk of AS by about 20%, while ulcerative colitis increased the risk by about 17%.  IBD and its subtypes were associated with an increased risk of peripheral forms of SpA, including psoriatic and reactive arthritis.

The reverse, however, was not true. No SpA subtype was found to have a causal effect on any IBD subtype. This one-way relationship had been observed in previous studies, the researchers noted.

The exact cause of the link between IBD and SpA “remains unclear,” the team wrote.

Scientists have proposed a number of mechanisms that may explain the link. Dysregulation of the microbes in the gut during IBD, for example, may activate immune cells that subsequently move out of the gut to the joints, where they cause inflammation, in a so-called “gut-joint axis.”

Because everyone in the study was of European descent, the results may not apply to a broader population, the researchers cautioned.

“Further longitudinal studies with larger scaled data of different ancestries are necessary to explore the specific effects of IBD on the onset and progression of SpA,” they wrote.

“Nonetheless, we truly hope this study contributes to providing new prospection on the optimization of screening and early diagnosis of SpA in IBD patients, so a timely preventative strategy can apply,” the team noted.