Study Examines Differences in Gut Contents of Male, Female Ankylosing Spondylitis Patients

Gender-based differences in fecal metabolites in ankylosing spondylitis patients may provide clues about differences regarding male versus female disease progression.

The study with that finding, “GC-MS-based fecal metabolomics reveals gender-attributed fecal signatures in ankylosing spondylitis,” was published in Scientific Reports.

There are a number of differences in how ankylosing spondylitis affects males and females. Males are two to three times more likely to develop the disease, but females tend to have more severe disease and to have involvement of the peripheral joints (hips and shoulders). Females also tend to be diagnosed at older ages. However, the mechanisms underlying how the disease progresses differently between sexes aren’t very well understood.

Ankylosing spondylitis frequently involves gut inflammation, and differences in gut bacteria have been implicated in the disease — though the cause isn’t totally clear. Researchers now wondered whether differences in the gut might help explain some of the sex-based differences in the disease.

To address this question, they investigated fecal metabolites (yes, the contents of poop).  Samples were collected from 38 healthy controls (20 males and 18 females) and from 49 ankylosing spondylitis patients (26 males and 23 females).

The researchers used gas chromatography-mass spectroscopy, a technique that’s particularly good at identifying small molecules, like the kind different types of gut bacteria are likely to produce. In all, the researchers identified 84 compounds in all the samples. Then they compared levels of these compounds between the controls and the ankylosing spondylitis patients, both as a whole and based on sex.

The differences between patients and controls were pretty big, especially for fats and organic molecules called alkanes. However, there weren’t many differences between males and females who had the same disease status — that is, whether or not a person had ankylosing spondylitis affected their fecal metabolites to a much greater extent than the person’s sex.

The researchers did identify a few specific molecules that were different between males and females with ankylosing spondylitis. However, these differences were scant enough that they couldn’t totally rule out the possibility it was just an error in their measurements, rather than a true difference.

They did note that a few more metabolites were distinct between males with or without ankylosing spondylitis than in females. The researchers speculated  these differences might be related to sex-based differences in the progression of disease, but more research will be needed to test this idea.

“Nevertheless,” investigators concluded in the paper, “this study further indicates that AS [ankylosing spondylitis] differs between males and females and provides new directions for exploring the mechanisms of the differences in AS features between males and females.”