Out of the 25 patients checked again for the study, 14 are still alive. (Shutterstock)
A major scientific study has concluded that there is no mysterious brain disease spreading across New Brunswick, despite earlier alarming claims. Published in the Journal of the American Medical Association (JAMA), the report says that patients once believed to be suffering from an unknown neurological condition were, in fact, misdiagnosed.
Toronto-based neurologist Dr. Anthony Lang, along with 12 other experts, reassessed 25 of the 222 patients initially flagged by Moncton neurologist Dr. Alier Marrero. They found all the cases could be linked to known illnesses, including Alzheimer’s, Parkinson’s, traumatic brain injuries, cancers, or functional neurological disorders. Lang stated the odds of these cases pointing to a new disease were "less than one in a million," strongly suggesting there was no unknown condition at play.
The research team involved professionals from the University of Toronto and Horizon Health Network in New Brunswick. They also dismissed environmental factors like heavy metals or herbicides, which some believed could be the cause. The symptoms were too varied, ranging from hallucinations to memory loss, making it impossible for one environmental toxin to explain them all.
Lang became involved in the case after hearing about a possible mystery disease that lacked scientific evidence. He noted that if a new disease truly existed, more medical professionals across Canada would have raised alarms, not just one.
The study also highlighted problems in the original assessments. Many diagnoses were based on incorrect or overly interpreted test results. For example, EEGs — brain scans — were frequently labelled as abnormal, even when findings didn’t suggest disease. The study strongly recommends that any patient with an unclear neurological diagnosis should seek a second opinion. Sadly, many of Marrero’s patients have refused to do so.
Dr. Marrero, who was not consulted during the research, disagrees with the study. He claims the investigation was too limited and did not consider key environmental data or rare biological markers found in several patients. He still believes that a larger investigation, including soil, water, and air testing, is necessary.
Despite the recent findings, New Brunswick's health officials plan to continue their own probe. The province’s chief medical officer, Dr. Yves Léger, confirmed that their full report will be released this summer.
An earlier study from 2021 had already found no shared environmental or behavioural patterns among the patients. Another review in 2022 by a group of six neurologists also concluded that many patients originally diagnosed with the mystery disease actually had other known illnesses.
Of the 25 patients reassessed in the JAMA report, 14 are still alive and underwent fresh evaluations by independent specialists. These second assessments revealed that initial symptoms were often misunderstood or recorded inaccurately. Some had symptoms thought to be new and severe, but turned out to be long-standing or milder than reported.
Supporters of Dr. Marrero, including patient advocate Stacie Quigley Cormier, remain unconvinced. Cormier says her stepdaughter, Gabrielle, has rare proteins in her system and symptoms that don’t fit common diagnoses. She and others believe the concentration of rare disorders within families and geographic areas needs closer attention.
She fears that dismissing these cases could leave many patients without proper answers. According to Cormier, Marrero is one of the few doctors actively investigating all possible causes, including rare immune markers and environmental exposure.
The study noted that out of 66 patients offered a second opinion, only 14 agreed. The rest chose to stay under Marrero’s care. Researchers believe that reluctance to seek a second diagnosis may stem from emotional attachment to the original doctor, concerns about the healthcare system, or a simple lack of access.
The researchers argue that misinformation and early misdiagnoses have fed public fears, especially during a time when healthcare trust has weakened. They caution that confusion between facts and fear has likely made the situation worse for patients.
