The parents of children diagnosed with a rare disease are warning parents and doctors to watch for its confusing symptoms, anxious to spread the word about the new and confusing illness.

The illness is called "anti-NMDA receptor encephalitis" and was identified only four years ago. But the condition is often getting missed because it can so easily be confused with everything from brain tumours to psychiatric illnesses.

Tony and Cheryl Liuzza's daughter Jayden came down with the disease two years ago. Before falling ill, Jayden was a healthy and chatty 3-year-old. So when she developed an odd walk, her parents thought she must have injured herself.

But days later, her condition worsened. Jayden's temperament changed and she began crying a lot for no apparent reason. Her walking got worse and then her legs started twitching.

The twitching eventually moved up her body from her legs to her arms and into her face.

The little girl who was once a precocious talker began telling the same story over and over again and she began to suffer from episodes her parents mistook for night terrors.

"She would fall asleep for 10 minutes then wake up screaming, holding her head and rolling all over the bed. She would lash out at her father and me, hitting, biting and throwing toys at us," Cheryl told CTV News in an email.

Jayden was brought to The Hospital for Sick Children in Toronto, but doctors were baffled over what was wrong with her.

Most of the toddler's tests came back normal. She went through MRIs, EEGs, ultrasounds and lumbar punctures. Everything was normal except the EEG which showed some slowing on the right side of her brain and the lumbar puncture, which showed 13 white blood cells in her spinal fluid.

For weeks, experts in neurology, rheumatology, and infectious diseases examined Jayden and tried to figure out what was wrong. But she remained a medical mystery.

All the while, Jayden's condition continued deteriorating to the point that she stopped eating and walking and was having frequent seizures.

Finally, one of her doctors remembered reading about the research of Dr. Josep Dalmau at the University of Pennsylvania School of Medicine who was investigating a brand new disease. The hospital sent Jayden's spinal fluid to Dr. Dalmau.

He confirmed that her fluid tested positive for rare antibodies called "anti-N-methyl-D-aspartic acid receptor." That confirmed it: she had anti-NMDA receptor encephalitis.

The illness, formally identified in 2007, is an autoimmune disease in which the immune system goes haywire, ordering the brain to attack the body.

Its early symptoms of psychosis, hallucinations and memory loss can be so baffling, patients are often misdiagnosed with a mental illness. It is only when symptoms like seizures and language deterioration appear that doctors begin to suspect something else.

Nesrin Shaheen's daughter, Sonia, appears to be the first patient in Canada who was diagnosed with the illness. Sonia was admitted to the Children's Hospital of Eastern Ontario in January 2008, after the then-12-year-old began acting bizarrely and had difficulty speaking and walking.

"All she was able to say was ‘Mama, mama,' Although she might have been able to take a few steps, she would eventually collapse and fall down to the floor," her mother remembers.

After six agonizing weeks of tests, MRIs and even a brain biopsy, Sonia was finally diagnosed.

What doctors have learned so far about anti-NMDA receptor encephalitis is that most cases appear in young women or children. In a large number of cases, non-cancerous tumours are found on the ovaries or testicles.

One theory is that the tumours spark the condition. But in many patients, mostly the younger ones, a tumour is never found. In both Jayden and Sonia's cases, doctors didn't find tumours.

Removing the tumours is usually the first step in treatment. The condition is then treated with rituximab or cyclophosphamide, which are immunotherapy drugs used in leukemia and lymphoma patients.

Other treatments include intravenous immunoglobulin (IVIG), a blood product often used in treating autoimmune disorders. High doses of steroids can help reduce the inflammation in the brain. Recovery is long and patients are generally hospitalized for anywhere from a month to a year.

At least 22 cases have now been diagnosed in Canada, but studies have shown it's being misdiagnosed or undiagnosed, and many patients miss getting the lifesaving treatment they need.

The largest study of 400 cases has shown that death or severe deficits currently occur in about 25 per cent of patients.

Jayden is much better now and has improved to the point where one would never know she was once so sick. But Sonia has had three relapses since her first illness. She's currently feeling well and is back to playing guitar.

"I think I am really lucky because I know that people can die of this sickness. A few years ago, they could not diagnose it or they could not diagnose it fast enough and did not get the treatment fast enough.

"So I think I am lucky. I am really lucky," she says.

With a report from CTV medical specialist Avis Favaro and producer Elizabeth St. Philip

Sonia's mother Nesrin has started a Canadian support group on Facebook called Anti NMDA receptor Encephalitis in Canada/Encephalite Anti NMDA au Canada to offer support to family members of those afflicted.