According to new research, people with multiple sclerosis are far less likely than those without to have the molecular hallmarks of Alzheimer’s disease.

Washington University School of Medicine in St. Louis researchers recruited 100 patients with MS to take a blood test, using a new FDA-approved blood test known as PrecivityAD2, with 11 of the patients also undergoing PET scans. The blood test is highly effective at predicting the presence of amyloid plaques in the brain. Such plaques are an indicator of Alzheimer’s disease, which previously could only be verified with brain scans or spinal taps. Their results were compared with the results from a control group of 300 individuals who did not have MS but were similar to those with MS in age, genetic risk for Alzheimer's, and cognitive decline.

The study’s authors found that 50 percent fewer MS patients had amyloid pathology compared to their matched peers, based on this blood test. This finding supported observations that Alzheimer’s appeared to be less likely to develop among those with MS. The researchers also found that the more typical the patient’s MS history was, in terms of age of onset, severity, and overall disease progression, the less likely they were to have amyloid plaque accumulation in that patient’s brain compared with those with atypical presentations of MS.

This suggests there is something about the nature of MS itself that is protective against Alzheimer’s disease, which researchers are planning to investigate. MS patients generally have multiple flare-ups of the illness during the course of their lifetimes. During these flare-ups, the immune system attacks the central nervous system, including within the brain. It’s possible that this immune activity also reduces amyloid plaques, the researchers said.

The study’s authors have begun the next steps of this research, both to tease out the possible human genetics involved, as well as to test amyloid plaque development in animal models representing MS.

The study was published in the Annals of Neurology.