Prion diseases comprise several conditions. A prion is a type of protein that can trigger normal proteins in the brain to fold abnormally. Prion diseases can affect both humans and animals. They are sometimes spread to humans by infected meat products. In many cases, the source of the abnormal protein is unknown. The most common form of prion disease that affects humans is Creutzfeldt-Jakob disease (CJD).

Prion diseases are rare. About 300 cases are reported each year in the U.S.

Types of prion diseases include:

• CJD. A person can inherit this condition. In that case, it's called familial CJD. Sporadic CJD, on the other hand, develops suddenly without any known risk factors. Most cases of CJD are sporadic. They tend to strike people around age 60. Acquired CJD is caused by exposure to infected tissue during a medical procedure, such as a cornea transplant. Symptoms of CJD (see below) quickly lead to severe disability and death. In most cases, death occurs within a year.
• Variant CJD. This is an infectious type of the disease. It is related to “mad cow disease.” Eating diseased meat may cause the disease in humans. The meat may cause normal human prion protein to develop abnormally. This type of the disease often affects younger people and is becoming less common.
• Variably protease-sensitive prionopathy (VPSPr). This is also extremely rare. It is like CJD. But the protein is less sensitive to digestion. It is more likely to strike people around age 70 who have a family history of dementia.
• Gerstmann-Sträussler-Scheinker disease (GSS). This type is extremely rare. It occurs at an earlier age, typically around age 40.
• Kuru. This disease is seen in New Guinea. It's caused by eating human brain tissue contaminated with infectious prions. Because of increased awareness about the disease and how it is transmitted, kuru is now rare.
• Fatal insomnia (FI). This is a rare hereditary disorder. It causes trouble sleeping. There is also a sporadic form of the disease that is not inherited.

Normal prion protein is found on the surface of many cells. Prion diseases occur when this protein becomes abnormal and clumps in the brain. It then causes brain damage. This abnormal buildup of protein in the brain can lead to memory problems, personality changes, and trouble with movement. Experts still don't know a lot about prion diseases. But unfortunately, these disorders are often fatal.

You may be at risk for prion diseases if you:

• Have a family history of prion disease.
• Eat meat infected by “mad cow disease.”
• Are infected by contaminated corneas or medical equipment.

Symptoms of prion diseases include:

• Rapidly developing dementia.
• Difficulty walking and changes in gait.
• Jerking movements of the muscles.
• Hallucinations.
• Muscle stiffness.
• Confusion.
• Fatigue.
• Difficulty speaking.

Prion diseases are confirmed by taking a sample of brain tissue during a biopsy or after death. But given the risks of a brain biopsy, a number of other tests are often done instead. These can help diagnose prion diseases such as CJD or rule out other diseases with similar symptoms. Prion diseases should be considered in all people who have dementia that is quickly getting worse.

The tests include:

• MRI scans of the brain.
• Spinal tap (lumbar puncture) to take samples of fluid from the spinal cord.
• Electroencephalogram, which is a painless test that looks at brain waves by placing electrodes on the scalp.
• Blood tests.
• Nervous system and visual exams to check for nerve damage and vision loss.
• Genetic tests to look for known hereditary causes of prion disease. This is especially important if other family members are affected.

Prion diseases can't be cured. But certain medicines may help slow their progress. Medical care focuses on keeping people with these diseases as safe and comfortable as possible, despite worsening and debilitating symptoms.

Properly cleaning and sterilizing medical equipment may prevent the spread of the disease. If you have or may have CJD, don't donate organs or tissue, including corneal tissue. Newer regulations that govern the handling and feeding of cows may help prevent the spread of prion diseases.

As prion diseases progress, people with these diseases generally need help taking care of themselves. In some cases, they may be able to stay in their homes. But they eventually may need to move to a care facility.

• Prion diseases are very rare.
• Diagnosis is difficult but should be considered in all people whose dementia is quickly getting worse.
• Symptoms can progress rapidly, requiring help with daily needs.
• Prion diseases are always fatal.

Tips to help you get the most from a visit to your doctor:

• Know the reason for your visit and what you want to happen.
• Before your visit, write down questions you want answered.
• Bring someone with you to help you ask questions and remember what your doctor tells you.
• At the visit, write down the name of a new diagnosis and any new medicines, treatments, or tests. Also write down any new instructions your doctor gives you.
• Know why a new medicine or treatment is prescribed and how it will help you. Also know what the side effects are and when they should be reported.
• Ask if your condition can be treated in other ways.
• Know why a test or procedure is recommended and what the results could mean.
• Know what to expect if you do not take the medicine or have the test or procedure.
• If you have a follow-up appointment, write down the date, time, and purpose for that visit.
• Know how you can contact your doctor if you have questions.