A woman with a mysterious brain disease developed memory loss, a stutter, and tremors. She goes to bed every night in fear.

• Carol Clark is one of 48 people in Canada who developed a mysterious brain disease.
• She stutters, has memory loss, and lost a significant amount of weight.
• There are no known causes of the disease, but researchers are investigating.

At first, Carol Clark, 75, had flu-like symptoms and rapidly lost weight. Now she forgets long conversations she had a just a few days prior, according to her daughter, Joanne Graves.

Clark is one of 48 people in Canada's New Brunswick province to have developed a mysterious brain disorder that's suspected to have caused six deaths, Dr. Alier Marrero, a neurologist leading New Brunswick's investigation, told the BBC.

The cluster of cases became public in March when Radio-Canada and CBC got a leaked memo from health officials sent to local doctors. The memo alerted doctors to be aware of patients showing symptoms of Creutzfeldt-Jakob disease, including blurred vision, hallucinations, or disorientation. While the mysterious disorder bears similarities to Creutzfeldt-Jakob, it's not the same disease.

There's no known cause or treatment.

A no-name mysterious brain disorder

The cluster of cases surfaced in 2018, the same year Clark moved to New Brunswick, but doctors believe one case occurred in 2013.

Patients first came in with pains, spasms, and behavioral changes, and the symptoms progressed to impaired cognitive abilities, muscle wasting, drooling, hallucinations, and tooth-shattering over the next 18 to 36 months, according to Marrero.

These are some of the symptoms Clark started to have in January 2020.

"The muscle mass, it was just falling off her," Graves said.

Clark's legs and arms felt heavy, too, which prompted several trips to the hospital. But it wasn't until June 2020, when her hands and arms began having tremors, that she was referred to Marrero.

Although an MRI revealed that her frontal left lobe "changed," Graves said, tests, scans, and spinal tap didn't lead to a diagnosis. She tested negative for Creutzfeldt-Jakob disease.

"They never put a word on it, a name on it, because let's face it, they still haven't. They've just called it the mystery neurological disease," Graves said.

A leaked memo revealed a larger trend at play

Roger Ellis is another New Brunswick resident who contracted the mysterious brain disorder.

Prior to getting the disease, Roger Ellis, now in his 60s, led a healthy life in New Brunswick's bucolic Acadian peninsula. But in June 2020, he had a seizure. Ellis's son, Steve Ellis, said his father's health took a downward turn.

"He had delusions, hallucinations, weight loss, aggression, repetitive speech," Steve Ellis told the BBC. "At one point he couldn't even walk. So in the span of three months we were being brought to a hospital to tell us they believed he was dying - but no one knew why."

Similar to Clark, Roger Ellis underwent numerous tests and scans, and also tested negative for Creutzfeldt-Jakob disease.

Roger Ellis was left without a diagnosis, and it wasn't until the leaked memo emerged that he younger Ellis realized his father was part of a larger trend.

Investigator are searching for causes behind the mysterious disorder

Experts in neurology, environmental health, and zoonotics are working to find a cause behind the mysterious condition.

One possibility is that patients were exposed to environmental toxins. Investigators are studying excitotoxins, which were associated with a food poisoning case in a neighboring province in 1987, and beta-methylamino-L-alanine (BMAA), which is believed to cause Alzheimer's and dementia, according to one study published in 2009.

Clark goes to bed worrying she won't be able to walk the next day

Roger Ellis is now in a specialized home where he gets assistance with daily activities. Although his condition has stabilized, he still has sleep and speech problems.

Clark is taking Clonazepam, a sedative used to treat anxiety and seizures. Graves said her mother's condition has stabilized, but goes to be every night fearing that she won't be able to walk or talk the next day. Clark also stutters and wears layers of clothing to cover her weight loss.

"I call her an onion," Graves said.

Graves is frustrated that the cluster of cases wasn't public earlier on, as more awareness could have helped her mom to get treated faster.

"Maybe if it was made more public, that they would have possibly looked into her earlier, and she may not be in the situation that she's in," Graves said.