- 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.
Proteins are tiny working parts made by the cells of the body. Each one folds into a particular shape, and that shape lets it do its job.
What is prion protein?
Everyone makes a protein called prion protein. The instructions for it are in a gene called PRNP. In its normal form it is thought to help protect nerve cells and to help them pass signals to each other.
What makes a prion different?
A prion is a copy of this same protein folded into the wrong shape. The misfolded form tends to clump together, and it is hard for the body to break down.
How does it cause harm?
A misfolded copy acts as a template. Normal copies of the protein that meet it fold the same wrong way, and those new misfolded copies can do the same to others. Over time the misfolded protein builds up in the brain. Nerve cells stop working properly and are lost, and under a microscope the affected brain tissue shows tiny holes, which is why these illnesses are also called spongiform diseases.
Is a prion a germ?
No. A prion is very different from a virus or a bacterium. 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. Is CJD contagious? explains how prion disease can and cannot pass between people.
What does this mean for someone who is ill?
Illnesses caused by prions are called prion diseases. They are fatal, and at present there is no cure. This is very hard to read, and support is available. Palliative and hospice care describes the care that keeps a person comfortable, and support groups lists people who can talk with you.
Nothing on this page can tell you what is happening to a particular person. A neurologist is the right person to ask about symptoms or test results.
Prion diseases also affect animals, which is covered under animal prion diseases. For the science in more depth, see protein misfolding in the research section.