What was the 'New Brunswick Neurological Syndrome of Unknown Cause'?

It was a cluster of 500 patients in New Brunswick, Canada, diagnosed by neurologist Alier Marrero with a mysterious, unnamed brain disease exhibiting diverse symptoms.

Who is Dr. Alier Marrero?

Dr. Alier Marrero is a Cuban-born neurologist in New Brunswick who identified and diagnosed the cluster of patients with a suspected unknown neurological condition.

What did the JAMA study conclude about the New Brunswick cluster?

The May 2025 JAMA study concluded that there was no new mystery disease and that the patients suffered from previously known conditions, citing serial misdiagnosis by Dr. Marrero.

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Canada's Mystery Brain Disease: A House of Cards?

11 Jan

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Summary

Hundreds of Canadians diagnosed with a mystery brain disease experienced diverse symptoms.
A research paper concluded no new disease existed, calling the cluster a 'house of cards'.
Some patients now pursue medically assisted dying due to prolonged health issues.

Canada's Mystery Brain Disease: A House of Cards?

In New Brunswick, Canada, a cluster of 500 individuals was diagnosed with a mysterious neurological condition starting in early 2019. Neurologist Alier Marrero documented a wide array of symptoms, initially suspecting Creutzfeldt-Jakob Disease (CJD) before identifying a potential unknown syndrome.

However, a major research paper published in May 2025 in JAMA concluded that all patients studied had previously known conditions, such as functional neurological disorder or dementia, suggesting serial misdiagnosis by Dr. Marrero. This study, involving 14 live patients and 11 autopsies, dismissed the existence of a new disease, labeling the cluster a 'house of cards'.

The findings have deeply divided patients and advocates. While some have found closure with established diagnoses, many remain loyal to Marrero, believing their symptoms are real and potentially linked to environmental toxins. The controversy continues, with some patients exploring medically assisted dying, highlighting the profound impact of the unresolved mystery.