Scientists Solve Mysterious Brain Disease in Canada

A new study doesn't entirely rule out the possibility that a mystery disease has struck hundreds of people in Canada, but it puts the risk at roughly one in a million. Published Wednesday in JAMA Neurology, the evaluation of 14 living and 11 deceased patients identified as part of the New Brunswick cluster concludes they suffered from "well-known, previously misdiagnosed neurological conditions," including Alzheimer's, Parkinson's, metastatic cancer, functional neurological disorder, traumatic brain injuries, and post-concussion symptoms, per NBC News and the CBC. "We really felt we had a good explanation for 100% of the cases," study author Dr. Anthony Lang, a neurologist at Toronto Western Hospital's Krembil Brain Institute, tells NBC.

The paper backs up years-old findings. In 2022, a committee including independent neurologists reviewed the cases of 48 patients, identifying "potential alternative diagnoses" for 41. But "sadly, the physician involved continues to believe and convince the patients and families that they have a mysterious illness," Lang says, referring to Moncton neurologist Dr. Alier Marrero, who's diagnosed hundreds of patients in seven provinces as having a "neurological syndrome of unknown cause." Researchers noted 52 patients in the cluster refused second opinions and 42 didn't respond to communication, possibly due to misinformation. Marrero has suggested an environmental toxin, but that "could never have explained this broad variety of neurological abnormalities," Lang tells the CBC.

In a statement, Marrero says he's "in profound disagreement" with the findings of a study examining a "small number" of patients, per the CBC. But despite the small sample size, "when we did the statistics … the chances of any of those other individuals having a mystery disease was less than one in a million," Lang tells the outlet. "I think that if there really had been a mystery disease with those numbers, we would have been hearing from more than a single physician." The study calls for "education, reassurance, and mental health support" for patients who believe "a potentially fatal mystery disease continues to affect them." A provincial investigation into the cases is ongoing. (More Canada stories.)