- Normal proteinEveryone makes prion protein. It sits on the surface of cells.
- A wrong foldSome of the protein folds into the wrong shape.
- It spreads its shapeThe misfolded form causes more protein to misfold.
- Build-upMisfolded protein gathers and is hard to clear.
- Nerve cells are damagedThis causes the symptoms of the illness.
- About 85%Sporadic, no known cause
- About 5 to 15%Inherited
- About 1 to 2%Acquired, such as through medical care
Approximate shares of cases, from CDC and MedlinePlus. Sources differ slightly.
Everyone makes prion protein. It sits on the surface of cells, including nerve cells in the brain, and for almost everyone it causes no trouble at all.
What is going wrong in the brain?
Prion disease begins when some of that protein folds into the wrong shape. The misfolded form is hard for the body to clear away. It builds up, and the nerve cells around it are damaged, which is why the symptoms are those of a brain illness.
A prion is a misfolded protein. Antibiotics and antiviral medicines have no effect on it, and it survives heat and radiation strong enough to kill bacteria and viruses. That is why hospitals use special cleaning rules for a few kinds of surgery.
Which diseases are in this group?
CJD is the most common prion disease in people. Variant CJD is a separate and much rarer disease. The group also includes kuru, sporadic fatal insomnia and variably protease-sensitive prionopathy, along with the inherited forms: familial CJD, Gerstmann-Straussler-Scheinker syndrome and fatal familial insomnia. The full list is on our diseases page.
Animals have prion diseases too. Bovine spongiform encephalopathy, often called mad cow disease, affects cattle. Chronic wasting disease affects deer, elk, moose and reindeer.
Why do they happen?
In about 85 of every 100 cases the protein misfolds with no known cause. These are called sporadic.
Between about 5 and 15 in every 100 cases are inherited. Here a person has a change in PRNP, the gene that carries the instructions for prion protein, passed on in a family.
A small number, about 1 or 2 in every 100, followed contact with prions during medical care, through tissue grafts, surgical instruments or growth hormone made from human tissue before the mid 1980s. Variant CJD is linked to eating beef from cattle with BSE.
How rare is this?
About 1 to 2 people in a million develop a prion disease each year. Estimates for the United States range from about 350 to 600 cases a year.
How does the illness usually go?
Symptoms are usually slight at first and then get worse quickly, over weeks and months. Most people live for months to about a year after symptoms begin, and some of the inherited forms run a longer course, nearer two years.
Is there a cure?
Not at present. Prion diseases are fatal, and no treatment stops them. This is very hard to read, and you do not have to take it all in at once.
Care is aimed at comfort, at keeping symptoms under control and at support for the people doing the caring. A palliative care team can be asked in early, long before the last weeks, and many families find that helps. Palliative and hospice care explains what they do, and support groups lists people who can talk with you.
Who should I ask about my own situation?
Nothing on this page can tell you what is happening to a particular person. Questions about symptoms, test results or whether a condition runs in a family belong with a neurologist, and questions about inheritance belong with a genetic counsellor, who comes before any genetic test. If you are weighing a test, choosing not to be tested is a valid choice.
For how the misfolding works in more depth, see what are prion diseases: more detail, what is a prion and our mechanisms overview.