Types of CJD
There are 4 main types of CJD, which are described below.
Sporadic CJD
Sporadic CJD is the most common type.
The precise cause of sporadic CJD is unclear, but it's been suggested that a normal brain protein changes abnormally ("misfolds") and turns into a prion.
Most cases of sporadic CJD occur in adults aged between 45 and 75. On average, symptoms develop between the ages of 60 and 65.
Despite being the most common type of CJD, sporadic CJD is still very rare, affecting only 1 or 2 people in every million each year in the UK.
In 2014, there were 90 recorded deaths from sporadic CJD in the UK.
Variant CJD
Variant CJD (vCJD) is likely to be caused by consuming meat from a cow that had bovine spongiform encephalopathy (BSE, or "mad cow" disease), a similar prion disease to CJD.
Since the link between variant CJD and BSE was discovered in 1996, strict controls have proved very effective in preventing meat from infected cattle entering the food chain.
See preventing Creutzfeldt-Jakob disease for more information.
But the average time it takes for the symptoms of variant CJD to occur after initial infection (the incubation period) is still unclear.
The incubation period could be very long (more than 10 years) in some people, so those exposed to infected meat before the food controls were introduced can still develop variant CJD.
The prion that causes variant CJD can also be transmitted by blood transfusion, although this has only happened 4 times in the UK.
In 2014, there were no recorded deaths from variant CJD in the UK.
Familial or inherited CJD
Familial CJD is a very rare genetic condition where one of the genes a person inherits from their parent (the prion protein gene) carries a mutation that causes prions to form in their brain during adulthood, triggering the symptoms of CJD.
It affects about 1 in every 9 million people in the UK.
The symptoms of familial CJD usually first develop in people when they're in their early 50s.
In 2014, there were 10 deaths from familial CJD and similar inherited prion diseases in the UK.
Iatrogenic CJD
Iatrogenic CJD is where the infection is accidentally spread from someone with CJD through medical or surgical treatment.
For example, a common cause of iatrogenic CJD in the past was growth hormone treatment using human pituitary growth hormones extracted from deceased individuals, some of whom were infected with CJD.
Synthetic versions of human growth hormone have been used since 1985, so this is no longer a risk.
Iatrogenic CJD can also occur if instruments used during brain surgery on a person with CJD aren't properly cleaned between each surgical procedure and are reused on another person.
But increased awareness of these risks means iatrogenic CJD is now very rare.
In 2014, there were 3 deaths from iatrogenic CJD in the UK caused by receiving human growth hormone before 1985.
Introduction 