Creutzfeldt-Jakob disease

Creutzfeldt-Jakob disease (CJD) is a rare and fatal form of dementia, caused by abnormal prion proteins that are toxic to the brain.

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Creutzfeldt-Jakob disease (often abbreviated to CJD) is a rare and fatal form of dementia.

What is CJD caused by?

CJD is caused by a protein found in the brain called a prion. In its natural form, this type of protein is harmless. Prions are made by most body cells and doesn’t cause disease.

But in their abnormal form, prions are toxic to brain cells, causing disease and damage to the brain. One kind of damage is spongiform change, in which the brain tissue looks like a sponge with many tiny holes. Many of the brain’s nerve cells die, leading to symptoms like dementia.

Why these prions turn abnormal is still not understood, though researchers are working to figure this out.

How quickly does CJD progress?

It can be several years between when a person is exposed to CJD and when the first abnormal prions are formed.

Usually a mental or neurological problem appears first, and early symptoms can be mild. A family member is often the first to notice that a person is going through mood swings, social withdrawal or has a general lack of interest.

Once symptoms take hold, the disease progresses quickly. Eventually, a person affected by CJD loses the ability to move and speak, and will need full-time care.

Unfortunately, it’s rare that people with CJD live beyond a year. Most people affected will pass away within six months of the illness taking hold.


The majority of people living with CJD fall under two types, sporadic and familial. In rare cases, CJD can be accidentally transmitted from other people and animals, leading to iatrogenic and variant types.


Most diagnoses of CJD – about 90% – are considered sporadic, meaning they do not run in families. Sporadic CJD can affect older people without warning or explanation. The prion protein likely begins to form in one or a few brain cells and then spreads to the rest of the brain.

Sporadic CJD is found worldwide, mostly in people over 50. Canada, the United States, UK, Australia, and several European countries carefully monitor diagnoses of sporadic CJD. About one or two diagnoses typically occur per million people each year.

Since 1998, when monitoring began, 1007 Canadians have been diagnosed with sporadic CJD.


About 10% of other CJD diagnoses are inherited or familial, running in a family's genetic history. A genetic mutation can increase your chances of developing genetic prion diseases. These diseases mostly affect older people, though in some families CJD can develop at younger ages. However, some people with a genetic mutation never develop the illness.

Since 1998, 70 Canadians have been diagnosed with a form of familial CJD.


Infection with human prions can occur by accident through certain medical procedures involving human tissues. This kind of CJD is called iatrogenic, meaning it is caused by a medical treatment.

Most cases of iatrogenic CJD have been found in the United States, United Kingdom, France and Japan. To date, only six people have been diagnosed with iatrogenic CJD in Canada.


In very rare cases there are diagnoses of CJD that result from human exposure to bovine spongiform encephalopathy (BSE). You may know BSE as its more common name, Mad Cow Disease.

BSE is a prion disease found in cattle. When someone has been exposed to BSE and it causes dementia, it is known as variant CJD. People with variant CJD tend to be much younger than those with other types of CJD, often in their 20s.

Only two Canadians have ever been diagnosed with variant CJD, and both times they were living abroad.


So far, researchers have identified more than 50 variations of CJD across the major types. All of these variations can have different symptoms. Symptoms can even differ between two family members who both have CJD.

Sporadic CJD

People with sporadic CJD may experience any combination of the following symptoms:

  • Dementia (loss of memory and thinking abilities),
  • Ataxia (unsteadiness when walking or standing, marked clumsiness),
  • Myoclonus (sudden jerky movements),
  • Changes in behaviour (such as depression, irritability and anxiety),
  • Vision problems (including blindness),
  • Aphasia (loss of ability to speak or understand speech),
  • Stiffness of arms or legs and
  • Difficulty swallowing.

Familial CJD

Symptoms can differ enough in familial CJD that some genetic prion diseases have been given special names:

  • In genetic CJD, symptoms are similar to those of sporadic CJD.
  • Gerstmann-Sträussler-Scheinker disease (GSS) usually starts with clumsiness or unsteadiness when standing or walking, and later progresses to dementia. People living with this variation may survive for several years after symptoms start to show.
  • In fatal familial insomnia (FFI), the main symptom is a severe, progressive and untreatable form of insomnia. FFI leads to reduced control of basic bodily functions, such as blood pressure. Coma and death eventually follow.

Iatrogenic CJD

Symptoms of iatrogenic CJD are like those of sporadic CJD. Many people with iatrogenic CJD noticed difficulties with movement first before the onset of dementia.

Variant CJD

Since people with variant CJD tend to be younger, their early symptoms are often less common in other forms. These symptoms are:

  • Changes in behaviour (such as depression, irritability, anxiety),
  • Ataxia (unsteadiness when walking or standing, marked clumsiness) and
  • Persistent pain or other strange sensations.

Dementia tends to begin later on in people with variant CJD. Death usually occurs 13-14 months after symptoms begin.


CJD is difficult to diagnose, especially in the beginning. However, the following procedures can help detect whether the disease is present.

Detailed medical history

Because CJD develops so quickly, a detailed medical history can help the doctor determine when the person's signs and symptoms started.

Magnetic resonance imaging (MRI)

An MRI takes a picture of the brain. This picture can show signs of the disease, and tell the difference between sporadic CJD and variant CJD.

Electroencephalogram (EEG)

An EEG measures the brain’s electrical activity. Often, but not always, there is a specific EEG pattern that helps identify CJD.

Lumbar puncture

With a lumbar puncture, cerebrospinal fluid (CSF) can be taken from the person’s lower back and tested in the lab. The amounts of certain protein markers in the fluid, which indicate brain cell degeneration, are usually higher than normal in CJD. Other tests on the fluid can help determine if the person has a condition that isn’t CJD.

Blood tests

There is no useful blood test for CJD. However, a blood sample is often used to prepare DNA, which can be tested to diagnose genetic prion disease.

Brain autopsy

The only definitive way to tell if a person has CJD is to examine their brain tissue in an autopsy. See our page on brain donation for more information.

Risk factors

There are different risk factors for each type of CJD.

Sporadic CJD

As the name implies, sporadic CJD cannot be predicted. However, researchers are doing their best to study the disease and shed more light on possible risk factors.

Genetic prion diseases

As with any genetic disease, the risk of developing genetic prion disease can be passed down from parent to child. The chance that a parent will pass down genetic CJD is 50% for each child. If a person has a brother or sister with a mutation, there is a 50% chance that they have it too.

The risk of genetic CJD decreases with more distant relationship to an affected person. A family at risk for genetic prion disease needs medical support to use this knowledge in personal decisions.

Genetic counselling is strongly recommended for anyone who has questions about their genetic risk for prion disease, though there are some things you should know before participating in genetic testing.

If you have questions about genetic testing for CJD, you should contact the Creutzfeldt-Jakob Disease Surveillance System (CJDSS) at 1-888-489-2999.

Iatrogenic CJD

Thanks to advancements in scientific knowledge and medical technology, medical procedures involving human issue are safer than ever before. This greatly reduces the risk of iatrogenic CJD passing from one person to another.

Variant CJD

The Canadian government has implemented safety measures and regulates the beef industry to minimize the risk of human contact with BSE through food. With these safeguards, the risk of human exposure to BSE is now considered extremely low.


There is no known cure for CJD, no approved medical treatments to prevent it and no effective way to slow its progression. Care is supportive and focused on keeping the person as comfortable as possible.

More useful links and resources

Creutzfeldt-Jakob disease. Alzheimer Society of Canada. Our information on Creutzfeldt-Jakob disease (CJD) is also available in a downloadable, print-friendly PDF.

Creutzfeldt-Jakob Disease Surveillance System. Public Health Agency of Canada. The Creutzfeldt-Jakob Disease Surveillance System (CJDSS) tracks the diagnoses of CJD in Canada, including the latest statistics. If you think that you or someone you know may have CJD, the CJDSS is the organization to contact.

Prion diseases. Government of Canada. This government page gives more detail about prion diseases, of which CJD is the most common type.