Sporadic prion disease

The sporadic form of the disease, also known as sporadic Creutzfeldt-Jakob disease (CJD), or classical CJD, accounts for approximately 85% of all recognised prion disease. Sporadic CJD occurs in every country with a remarkably similar incidence: approximately one person in every million develops sporadic CJD per year.

What Causes Sporadic Prion Disease?

Sporadic prion disease occurs 'out of the blue', at random in the population. What initially triggers this 'chain reaction' in sporadic CJD is unknown, it may simply represent an unlucky event whereby this change occurs spontaneously in the brain and involves sufficient prion protein molecules to trigger off a self-sustaining process. An alternative hypothesis is that one or more cells in the body may have a mutation in the gene which encodes the prion protein and these cells then produce a faulty prion protein which will tend to form the rogue form spontaneously. This type of fault is called a 'somatic' mutation and is quite distinct from inherited mutations seen in the inherited prion diseases, where a faulty gene has been inherited from a parent (Refer to the inherited prion disease page). Somatic mutations are not passed on to children.

Characteristic Features of Sporadic Prion Disease

The disease usually affects people between the ages of 45-75, the average age of onset being around 65. The duration of the illness varies, for most people it is less than a year and may be as short as 6 weeks. For a minority, the illness duration can be up to 3 years.

Symptoms of the disease can vary though classically sporadic prion disease is recognised as a rapidly progressive dementia affecting many aspects of functioning. Typically there is an insidious onset followed by a very rapid decline.

Early non-specific symptoms may include dizziness, headaches, fatigue, sleep disturbance and weight loss. Behavioural symptoms such as mood swings and loss of interest may also be seen. Because of these initial symptoms the person may at first be thought to be suffering from depression or other psychiatric disease. Refer to the signs and symptoms page for further information.

Unusual Presentation of Sporadic Prion Disease

In a minority of people the illness can present in a different (atypical) way. A number of types of such atypical CJD are recognised; examples are of an illness in which the prominent features are a disturbance of balance and movement, or alternatively visual deterioration. Occasionally the disease will resemble a stroke, having an extremely sudden onset.