Causes and risk factors

In 85% of cases, prion diseases are sporadic and the healthy protein develops into a diseased protein form or prion for unknown reasons. The causes and risk factors for developing sporadic prion disease are currently unknown.  

10-15% of cases represent familial forms that are due to a genetic mutation that makes the healthy protein transform into the diseased prion more easily. There is a 50% chance of the genetic alterations that cause the disease being passed onto children. Patients with genetic forms usually have a family history of the disease, but there are some genetic cases where there is no known family history.  

In less than 1% of cases, the disease is acquired, and occurs when a pathogenic prion protein (which is altered and causes the disease) turns a healthy protein into a prion. A pathogenic prion protein or prion is a misfolded protein that transmits its shape to other proteins.   This is why it is known as an acquired or communicable disease. Only the following cases have been confirmed as being transmitted to humans so far:  

• Creutzfeldt-Jakob disease variant. By ingesting the meat and offal of cattle affected by bovine spongiform encephalopathy or ‘mad cow disease’. More than 90% of cases occurred in the UK in the 1990s and first years of the 21st century.  
• Iatrogenic Creutzfeldt-Jakob disease. Through medical procedures such as brain surgery, corneal transplants or injections of pituitary hormones extracted from cadavers in the late 20th century. This mechanism of transmission was eradicated by modifying procedures that prevent prion transmission.  
• Kuru. In cannibalistic rituals practised by tribes in Papua New Guinea. It is now considered to have been eradicated.