The Central Question

For years, a medical mystery has gripped the Canadian province of New Brunswick, with residents reporting a cluster of unexplained neurological symptoms. A new peer-reviewed study published in the Journal of the American Medical Association (JAMA) casts doubt on the existence of a novel brain disease, attributing the cases instead too a combination of misdiagnosis and misinformation.

However, this conclusion is unlikely to quell the fears of affected families, many of whom suspect environmental contamination as the root cause.

the JAMA Study: A Closer Look

The JAMA report is an self-reliant reassessment of 25 cases initially diagnosed by Dr. Alier Marrero, a moncton-based neurologist. These cases were drawn from a larger pool of 222 suspected patients.The study’s authors, affiliated with the University of Toronto, New Brunswick’s Horizon health network, and other Canadian institutions, concluded that the patients had been misdiagnosed.

According to the study, the individuals were suffering from:

• Common neurodegenerative diseases, such as Alzheimer’s and Parkinson’s
• Functional neurological disorder
• Traumatic brain injury
• Metastatic cancer

The study further stated that well-known conditions were identified in all 25 cases, including common neurodegenerative diseases, functional neurological disorder, traumatic brain injury and metastatic cancer, and that a study of 11 autopsy cases led to the conclusion that a new disease was extremely unlikely, with a probability less than .001.

Families Remain Skeptical

Despite the JAMA report’s findings, families of those affected remain unconvinced, suspecting that the study overlooks the possibility of environmental factors. Patient advocacy groups have rejected the idea of a new mystery illness, arguing rather that the cases are linked by environmental contaminants, though the researchers say they do not beleive the patients were made ill by exposure to something in the environment, such as herbicides or heavy metals like mercury.

Official Response and Previous Investigations

In 2021, health officials in New Brunswick initially raised concerns about more than 40 residents suffering from a possible unknown neurological syndrome, exhibiting symptoms similar to Creutzfeldt-Jakob disease. These cases were referred to Dr.Marrero after initial physicians were stumped by the symptoms.

However, in 2022, an independent oversight committee resolute that the patients had most likely been misdiagnosed and were suffering from known illnesses such as cancer and dementia. The committee’s final report concluded there was no cluster of people suffering from an unknown brain syndrome, effectively ending the province’s investigation.

Dissenting Voices

Despite the official conclusions, concerns lingered. A federal scientist reportedly worried there was something real going on in New Brunswick. Another said the investigation was shut down and that caseloads were higher than officially acknowledged. I don’t think it is indeed helpful to suggest or point to who or why – suffice to say that we were prepared to marshal both financial and human scientific resources to tackle the mystery, but they were declined, the scientist wrote.

According to a February 2025 letter from Dr. Marrero to federal and provincial officials, the number of patients suffering from unexplained neurological symptoms has since jumped to 507 across multiple Canadian provinces, including several under the age of 45.

Accusations of Misinformation and Inaccurate Assessments

The JAMA study suggests that misdiagnosis and misinformation become inextricably entwined and amplify harm exponentially, noting that more than half of the people eligible for the study declined to participate. The researchers also blamed inaccurate clinical assessments and an over-reliance on ancillary testing for perpetuating the idea of a mystery illness and said they found meaningful discrepancies in case histories.

Dr.Marrero’s rebuttal

Dr. Marrero has voiced strong disagreement with the study’s conclusions. In a statement, he said he is in profound disagreement with the study conclusions and has many questions regarding the methods and the content, adding that he was appalled that an investigation with a small number of patients has been conducted without his knowledge.

the Province’s Response and Future Plans

Premier Susan Holt has pledged a fresh and “thorough” investigation after taking office last last year. I think we need to be doing everything we can to shed some light on this and find a way to stop what’s making people sick, she said at the time.

New Brunswick’s chief medical officer of health, Dr. Yves Léger, stated that the JAMA study does not change his office’s intention to complete its own investigation into the 222 cases referred by Dr. Marrero. Updates will be posted on the province’s website, and a public report with recommendations is expected in the coming months.