Levels of suPAR Protein Linked to Myasthenia Gravis Severity

Measuring levels of a protein known as suPAR in the blood could be useful for assessing the severity of myasthenia gravis (MG), a pilot study reports.

The study, “Serum level of soluble urokinase plasminogen activator receptor (suPAR) as a disease severity marker of myasthenia gravis: a pilot study,” was published in the journal Clinical & Experimental Immunology.

suPAR — soluble urokinase plasminogen activator receptor — is a protein found in the blood that has been associated with inflammation in autoimmune disorders. Yet, whether suPAR may be a biomarker of disease activity in MG has not been assessed properly.

Now, researchers in Japan measured blood suPAR levels in 40 people with MG who were positive for antibodies against the acetylcholine receptor, the most common cause of MG. For comparison, suPAR levels also were measured in 30 people without MG (controls) — 15 healthy people and 15 with other diseases (e.g., spinocerebellar ataxia, Alzheimer’s disease and Parkinson’s disease).

The two groups were matched by age and sex. Average age in the MG group was 56.9 and disease duration was 21.9 months. Twenty-eight patients had generalized MG and 12 had ocular MG.

Blood suPAR levels were not significantly different in the two groups.

Ten patients had data available both before and after symptoms eased as a result of treatment with immunosuppressants. In these individuals, blood suPAR levels did not change significantly following treatment.

The researchers then constructed statistical models to look for associations between suPAR levels and various MG-relevant parameters. Blood suPAR levels significantly correlated with two measurements of disease severity: the MG activities of daily living (MGADL) scale, and the MG Foundation of America (MGFA) clinical classification. That meant that people with higher suPAR levels had more severe disease.

“Serum [blood] suPAR levels significantly correlated with MG severity scores,” the researchers wrote

In contrast, suPAR levels did not correlate with levels of anti-AChR antibodies or with clinical status after six months.

“Generally, anti-AChR antibody titers [levels] are not associated with MG severity, and our data showed no correlation between anti-AChR antibody titers and MGADL scale or MGFA,” the researchers added.

According to the team, the reason why suPAR levels were associated with disease severity among people with MG, but were not different between the MG and control groups, could be that suPAR itself is not directly involved in the onset of MG. Rather, it may exacerbate the disease once it begins. More studies will be needed to test the hypothesis.