- 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.
When a family hears this diagnosis, one of the first questions is often why it happened. For most people, doctors cannot give a specific reason. Nothing the person ate, did or failed to do is known to have caused it.
What are the main causes?
No known cause. About 85 in every 100 cases are called sporadic. The protein misfolds for reasons that are not understood.
Inherited. Between about 5 and 15 in every 100 cases come from a change in the PRNP gene, passed down in a family. Inherited prion disease explained describes this, and it opens with what to know before reading further.
Medical care. A very small number of cases, about 1 or 2 in every 100, followed contact with prions during medical treatment, such as tissue grafts, surgical instruments or growth hormone made from human tissue before the mid 1980s.
Variant CJD. This rare form is linked to eating beef from cattle with BSE.
Can you catch it from someone?
Ordinary contact with a person who has CJD does not pass it on. Is CJD contagious? explains this.
Who should I ask about my own situation?
This page cannot say why one particular person became ill. The treating neurologist can explain what is known in that case, and a genetic counsellor can talk through questions about family history, before any test.
More detail on causes gives the clinical picture. What are prion diseases? starts from the beginning.