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 brain disease that leads to dementia.

What is CJD caused by?

CJD is caused by a protein found in the brain called a prion. In its natural shape, this type of protein does not cause disease. Prions are made by most body cells and don't cause disease.

But if prion protein folds into the wrong shape, it is toxic to brain cells and causes disease. We still don't understand why some prion proteins change shape and become toxic to the brain. Researchers are working to try and find answers.

There are different types of prion-related diseases that can happen in humans and animals. Creutzfeldt-Jakob disease is the most common type of prion-related disease in humans.

How quickly does CJD progress?

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

Usually, a mental or neurological problem appears first. Early symptoms can be mild, sometimes like depression. A family member or friend is often the first to notice mood swings, social withdrawal or lack of interest.

Once symptoms start, CJD usually progresses quickly. Eventually, the person loses the ability to move, speak or care for themselves, and they will need full-time care.

Unfortunately, most people with this disease will die within six months after the illness began. Some can live as long as one year, and rarely longer.


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 typically occurs in older people without warning or clear reason. These cases appear unpredictably and cannot be linked to other cases. Sporadic CJD likely begins when prion protein forms an abnormal shape in one or a few brain cells. The abnormal shape probably spreads to the normal prion proteins in the rest of the brain. 

Sporadic CJD is found worldwide, mostly in people over 60. 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. These genetic changes are called mutations. These mutations are found in the gene that tells body cells how to make prion protein. Mutations increase the chance that prion proteins will fold into the wrong shape, becoming abnormal, and causing prion-related disease.

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


A small number if CJD cases have occurred after a person is infected with misfolded or abnormally shaped prion proteins from other humans or animals. Infection with human prions has occurred by accident through certain medical procedures involving human brain tissues. This kind of CJD is called iatrogenic.

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.


This type is very rare. Cases happen when humans are exposed to bovine spongiform encephalopathy (BSE). This encephalopathy is more commonly known as 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, and their timing can change greatly from person to person. 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. Or loss of memory and thinking abilities.
  • Ataxia. Or unsteadiness when walking or standing.
  • Myoclonus. Or sudden jerky movements.
  • Changes in behaviour. Such as depression, irritability and anxiety.
  • Vision problems. Including blindness, seeing double and/or hallucinations.
  • Aphasia. Or loss of ability to speak or understand speech.
  • Stiffness of arms or legs.
  • Difficulty swallowing.

Familial CJD

Many different are rare genetic variations have been linked to this type of CJD.

Symptoms can differ enough that some genetic prion diseases have been given special names, such as:

  • Genetic Creutzfeldt-Jakob disease: This has similar symptoms to sporadic CJD.
  • Gerstmann-Sträussler-Scheinker disease (GSS): Symptoms include clumsiness when standing or walking. Later symptoms progress 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. Or unsteadiness when walking or standing.
  • Persistent pain or other strange sensations.

Dementia tends to begin later on in people with variant CJD. Death usually occurs one to two years after symptoms begin.


CJD is difficult to diagnose, especially in the beginning. There is no test to accurately diagnose CJD in a living person. The best way to confirm whether a person has had the disease is to examine brain tissue via an autopsy. 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 trying to identify possible risk factors for sporadic CJD.

Familial CJD

  • People who are over the age of 50 are at greater risk, though these diseases can develop at younger ages.
  • People who have a mutation in the human prion protein gene are much more likely to develop prion diseases.
  • As with any genetic disease, the risk of developing genetic prion disease can be passed down from parent to child.
  • People who have a parent or sibling with the mutation are at greater risk than those who do not.
  • If a parent has a human prion protein gene mutation, the chance they will pass it down is 50% for each child. If a person has a sibling 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.

Genetic counselling is strongly recommended for anyone who has questions about their genetic risk for prion disease. Genetic counselling services are available in most large medical centres in Canada. 

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

  • Many risk factors for this type of CJD have now been reduced, as scientific knowledge and medical technology have improved since this type of Creutzfeldt-Jakob disease was first identified.
  • To reduce risk, hospitals use special procedures to ensure that medical and surgical instruments are safe to use on patients. Lab workers also take safety precautions when handling specimens during diagnostic testing procedures.
  • Also to reduce risk, funeral services workers follow their provincial regulations when handling the remains of a person suspected to have had Creutzfeldt-Jakob disease. It is important to discuss a diagnosis of this disease with the funeral director when making funeral arrangements.

Variant CJD

  • The main risk factor is being exposed to bovine spongiform encephalopathy (also known as mad cow disease).
  • Overall risk in Canada is now considered extremely low, as the Canadian government requires the national beef industry to follow certain safety measures to reduce risk.
  • Receiving a blood transfusion from someone with the disease also increases risk considerably. In the UK, there have been five people who were likely infected with variant CJD after receiving blood transfusions. The blood products were from donors who were healthy at the time of donation but developed the disease later.
  • To reduce the risk around blood transfusion, the Canadian blood donation system (among others) now avoids blood donations by people who may have Creutzfeldt-Jakob disease.


There is currently no known cure for CJD. There are no approved medical treatments to prevent it and no effective way to slow its progression. Researchers are working on this.

In terms of managing symptoms, supportive nursing care is recommended in middle and later stages to focus 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.

Canadian CJD Association. Non-profit organization to to bring support to families in their time of need by having the ability to put them in touch with the medical community who specialize and understand CJD.

Canadian Association of Genetic Counsellors. 

Last updated: May 16, 2023.