Creutzfeldt-Jakob Disease (CJD) Dr Trisha Macnair CJD is a rare disease that causes degeneration of nervous tissues, for example in the brain and spinal cord.

In this article

What is it? What causes it?

What are the symptoms? Who's affected?

What's the treatment?

CJD is a prion disease. Prions are infectious disease-causing agents that consist of a modified protein (unlike bacteria, for example, which are more complex whole cells). In some unique way, which isn't understood, prion proteins cause degenerative diseases of the nervous tissues (for example, brain, spinal cord and nerves), which are usually fatal.

There's an important genetic link to prion disease and the gene involved is known as the PRP gene. We all have the gene and it normally produces a protein, but this protein can change shape into a prion protein - a tough and sticky form that destroys the cells.

Why it changes into a prion isn't clear, but mutations of the PRP gene are an important part of the story in some types of CJD.

There are several different mutations of the PRP gene. One type first discovered in a group of Libyan Jews causes a specific and rarer type of CJD, while the typical form of CJD is due to a different mutation.

Different mutations in the PRP gene may lead to different prion diseases, such as Gerstmann-Straussler-Scheinker disease (GSS) or fatal familial insomnia.

As the prion proteins damage the brain, large spongy gaps appear in the brain tissue. This process may go on for some time before symptoms develop. Once prion proteins are present (whether they appeared sporadically or through an inherited faulty gene) they can be passed on through contact with infected tissue. This is rare but some cases of CJD have occurred, for example, when the prion proteins have been accidentally transmitted during treatment of a person with the older type of human growth hormone, which was extracted from donated brain tissue (this treatment is no longer used).

CJD may have been passed to humans through infected beef products. There appears to be a link between cattle infected with bovine spongiform encephalopathy (BSE) and a variant of the disease, vCJD, in young people.

But there are several types of CJD and infection isn't the only clue to this mysterious condition - it's not entirely clear how, but cases of CJD may be of an inherited, infectious or unknown origin.

Most cases of CJD - about 85 per cent - are sporadic, with no obvious cause. In other words, in most cases it can't be explained by anything other than random chance.

Early symptoms include memory loss, mood changes and loss of interest in life. This is followed by clumsiness, confusion, unsteadiness and slow or slurred speech.

As the weeks pass, movement becomes jerky and the limbs become shaky or stiff. Other problems, such as incontinence, develop and the person is increasingly unable to speak or move, until they lose awareness of their surroundings.

Death usually occurs within six months to a year, although progress of the disease can be slower.

One of the biggest problems with CJD is that it has a very long incubation period. A person may be infected without knowing it for decades before symptoms appear. During this time, the person carrying the infection may donate blood, which is unwittingly contaminated, or may have surgery, contaminating medical instruments. When passed from human to human in this way it seems to lead to problems much more quickly and vCJD may appear within a few years.

CJD can now be detected in samples taken from a person's tonsils. This will help to identify those people who are carrying the infection, and a pilot study for a national screening programme is currently being carried out by the Health Protection Agency.

CJD typically affects people over 55, although vCJD is found in much younger people.

Around 85 per cent of CJD cases are sporadic. This type affects about one in a million people.

There's no cure for CJD, although scientists are looking closely at several potential treatments including drugs already being used in other conditions. Supportive treatments can make life more comfortable for those affected.

Antenatal screening may be possible in those with the rarer inherited type of CJD.

This article was last medically reviewed by Dr Rob Hicks in January 2008