- 1Front of the brainThinking, planning, personality and mood
- 2Side of the brainMemory and finding words
- 3Deep centre, the thalamusSleep and body rhythms
- 4Back of the brainSight
- 5CerebellumBalance and coordination
A simplified picture. Prion disease can affect many areas, and which come first differs by person and by type of disease.
CJD is the most common prion disease in people, and it is still rare. About 1 to 2 people in a million die of it each year worldwide, which comes to about 500 to 600 cases a year in the United States.
What causes it?
Everyone makes prion protein. In CJD some of that protein folds into the wrong shape, gathers in the brain and damages the nerve cells around it.
Most cases, around 85 in every 100 reported, are sporadic, which means the misfolding began for reasons nobody yet understands. Nothing the person did or did not do caused it. About 5 to 15 in every 100 are inherited, through a change in the gene for prion protein. A small number came from contact with prions during medical care in the past, through tissue grafts, surgical instruments or growth hormone made from human tissue before the mid 1980s. Prion diseases sets the forms side by side, and causes and risk goes further into where each one comes from.
What does it do?
The main symptom is a quickly worsening loss of thinking and memory. Difficulty walking and with balance is common, as are sudden jerky movements of the limbs and changes in vision. Which symptom comes first varies between people.
Most cases are in older adults, with an average age in the late 60s, and cases under 30 are very unusual. The illness moves faster than other causes of dementia. Most people die within a year of the first symptoms, and for many it is a few months. That is a hard thing to read, and it is the reason specialist and palliative teams are brought in early. What to expect goes through it stage by stage, written with families in mind.
How is it diagnosed?
A neurologist puts together the history and examination with an MRI scan, usually an EEG, and tests on the fluid around the spinal cord. Local teams ask a national prion service for an opinion. Examining brain tissue is the only way to confirm the diagnosis, which in practice usually means after death, so most families are given a probable diagnosis and that is what care proceeds on. How prion disease is diagnosed walks through it.
Is there any treatment?
CJD is fatal, and at present there is no cure. There is no medicine that stops or reverses it. Treatment is directed at symptoms, including pain, agitation, jerky movements and difficulty sleeping, and at keeping someone comfortable and at home where that is what the family wants. This part of care makes a real difference, and it is worth asking for a palliative care or symptom control team early. Support groups lists people who can talk with you.
Research is active. As of its page updated through October 2026, the CJD Foundation lists an antisense drug from Ionis, which it says completed enrolment of one regimen in September 2026; the PRiSM trial run through NeuroNEXT with the Broad Institute, recruiting, with a presymptomatic arm reported open in October 2026; and a Regeneron programme for adults with symptomatic prion disease now listed on the trials register. The antibody PRN100 is listed as not currently enrolling. These are the sponsors’ own statements on those dates, and none of them is an available treatment. Current trials keeps the list, and CJD for researchers covers the science.
More depth, written for counsellors and clinicians, is at CJD: more detail. Fatal familial insomnia, an inherited prion disease with a different pattern, has its own page at fatal familial insomnia.
What is happening to one person, and what any test or family history means for them, is a question for their neurologist, and for a genetic counsellor where a gene is involved.