The battle over Canada’s mystery brain disease

Lead

In early 2019 physicians in New Brunswick flagged two cases of Creutzfeldt–Jakob disease (CJD), prompting an investigation that morphed into a much larger controversy. Over five years one neurologist, Dr. Alier Marrero, assembled a case series he believed described a new, fatal neurological syndrome; the caseload he identified rose from about 20 to roughly 500. A 2025 peer-reviewed study concluded the cluster reflected known conditions and misdiagnoses, but hundreds of patients, advocates and some clinicians reject that finding. The dispute has left families seeking answers, some pursuing medical assistance in dying, and a province preparing another review.

Key takeaways

• Initial trigger: Two confirmed CJD cases in New Brunswick in early 2019 led to the creation of a multidisciplinary working group to investigate possible contagion.
• Case growth: Dr Alier Marrero reported a cluster rising from ~20 early cases to about 500 people over five years, with a core group known as the original 48.
• Money and capacity: The Canadian Institutes of Health Research offered C$5 million in 2021 for a field investigation; New Brunswick declined the funding and scaled back the federal collaboration.
• Clinic and split: A Mind Clinic was set up in 2021; by the time Marrero was dismissed in August 2022, 105 patients were registered and 94 chose to remain under his care.
• JAMA study: A May 2025 Journal of the American Medical Association paper examined 25 cases (14 living patients, 11 autopsies) and concluded the probability of a novel disease was near zero.
• Diagnoses found: Reported alternative diagnoses include functional neurological disorder (FND), Alzheimer’s disease, Lewy body dementia, frontotemporal dementia and other established conditions.
• Tensions: Patients and advocates allege environmental poisoning (glyphosate/heavy metals) and a government cover-up; researchers and neuropathologists describe serial misdiagnosis and institutional failures.
• Human cost: At least one cluster patient used medical assistance in dying; others report worsening disability, long diagnostic odysseys and deep distrust of health institutions.

Background

The story began when two patients at a New Brunswick hospital were confirmed with Creutzfeldt–Jakob disease in early 2019. CJD is a rare, fatal neurodegenerative condition with public‑health implications, prompting formation of an expert group that included federal and provincial specialists. Dr Alier Marrero, a neurologist working in New Brunswick, told colleagues he had been seeing multiple patients with rapidly progressive, CJD‑like symptoms, many younger than expected, and he reported those cases to Canada’s CJD Surveillance System.

Over the next two years the caseload identified by Marrero expanded and media attention increased after a provincial memo in March 2021 alerted clinicians to a possible syndrome and encouraged referrals. High‑level federal scientists engaged, and the cluster acquired a provisional name: New Brunswick Neurological Syndrome of Unknown Cause. The CIHR proposed funding and resource support, and a specialist Mind Clinic was established.

Main event

As referrals multiplied, clinical opinion diverged. Some neurologists in the working group were intrigued; others grew wary of Marrero’s wide symptom lists and diagnostic approach. Neuropathologist Dr Gerard Jansen reviewed autopsies of several deceased patients and identified pathologies consistent with Alzheimer’s and Lewy body dementia, arguing that the files reflected many known diseases rather than a single new entity.

The controversy intensified when the provincial government curtailed collaboration with federal scientists and declined the CIHR’s C$5 million. Officials expressed concern internally about the informal working group and Marrero’s methods; critics said the decision to pull back fuelled distrust and suspicion of a political motive to avoid environmental scrutiny.

Patients most loyal to Marrero described him as empathetic and exhaustive in testing, while others who sought second opinions at the Mind Clinic received conventional diagnoses and multidisciplinary care. By August 2022 Marrero was dismissed from the clinic; 94 of 105 patients chose to continue with him rather than stay under clinic oversight, further fracturing the clinical record and care pathways.

In May 2025 a JAMA paper led by Dr Anthony Lang and colleagues examined 25 cases (14 living patients and 11 autopsies) and reported that all could be explained by known neurological, psychiatric or medical conditions, concluding the apparent syndrome was the product of misdiagnosis and systemic factors including pandemic‑era distrust and media amplification.

Analysis & implications

Clinically, the episode highlights how charismatic clinicians and intense diagnostic focus can create case series that look like new syndromes when a variety of distinct disorders are grouped together. Functional neurological disorder (FND) in particular illustrates how real, disabling symptoms can be attributed to a psychosomatic mechanism, a diagnosis that carries stigma and is difficult to communicate effectively to patients and families.

Institutionally, the conflict underlines weaknesses in systems for adjudicating clinical uncertainty and for triaging large patient clusters: informal networks can accelerate attention, but lack of formal governance and transparent protocols risks fragmentation and harmful patient outcomes. The province’s decision to decline federal funding removed a potential path for coordinated investigation and left credibility gaps on both sides.

Politically and socially, allegations of environmental poisoning — centered on glyphosate and heavy metals — have mobilized local activism and legal pressure. Whether environmental exposure has any causal role will depend on rigorous exposure assessment and epidemiology; until those data are public and reproducible, claims of industrial culpability will remain contested and politicized.

For patients, the consequences are immediate: delayed correct diagnoses, inconsistent access to multidisciplinary care, expensive and sometimes risky treatments, and in at least one documented case the choice of medical assistance in dying without a confirmed terminal pathology. The episode raises ethical questions about clinical responsibility, informed consent in prolonged diagnostic processes, and research using patient records.

Comparison & data

These figures illustrate the divergence between a clinician’s case series and a formally analysed sample. The JAMA study used a smaller, selected subset (25 cases) and reached conclusions about diagnostic probability; Marrero’s broader total arises from his own clinic roster and referral network. Differences in sampling, case definition, and data access explain much of the disagreement.

Reactions & quotes

“I just kept documenting new cases, I kept seeing new people dying.”

Dr Alier Marrero (neurologist)

Patients describe Marrero’s bedside manner as attentive and validating, which strengthened their trust and amplified resistance to external critiques.

“What we have here is a case of misdiagnosis, evolving to misinformation, and sadly resulting in suffering for patients and families.”

Dr Anthony Lang (study lead, JAMA)

Researchers argue that rigorous case review and neuropathology show established diagnoses account for the presentations, and they stress methodological transparency.

“They pulled the plug because they just don’t want anybody looking.”

Kat Lanteigne (Bloodwatch, patient advocate)

Advocates and some patients interpret provincial decisions as evidence of concealment and call for a renewed, independent environmental inquiry.

Unconfirmed

• That a single industrial toxin (for example glyphosate) is the primary cause of the cluster remains unproven; current evidence is suggestive but not definitive.
• Allegations of an official cover‑up by New Brunswick authorities lack corroborating documentary proof; some government decisions are documented but motivations remain disputed.
• Precise numbers of patients with elevated glyphosate or heavy metals reported by Dr Marrero are not publicly verified; Marrero described an “unusual number, beyond 100,” but did not release exact figures.

Bottom line

The New Brunswick episode is a cautionary tale about how clinical uncertainty, media attention, institutional friction and community fear can combine to create a prolonged, polarizing public‑health controversy. Careful, transparent investigation — including independent exposure assessment, standardized case definitions, autopsy confirmation where possible, and open data — is the only reliable route to resolution.

For patients the priority should be accessible, evidence‑based multidisciplinary care and clear communication about diagnoses and prognosis. For policymakers, the lessons include the need for timely resourcing of investigations, dispute resolution mechanisms when clinicians and health systems clash, and protection for patients from both diagnostic error and premature lancings of unproven hypotheses.

Sources

• BBC — Investigative reporting on the New Brunswick cluster (media)
• Journal of the American Medical Association (JAMA) — May 2025 study on New Brunswick cases (peer‑reviewed journal)
• Canadian Institutes of Health Research (CIHR) (federal research agency; offered funding, 2021)
• Government of New Brunswick (provincial government; official statements and reports)