CJD and other prion diseases includes:
- Sporadic CJD
- Genetic CJD and other forms of inherited prion diseases
- Aquired forms of prion disease
- Iatrogenic CJD (iCJD)
- Variant CJD (vCJD)
Sporadic CJD a rapidly progressive disease that has no known cause but is believed to be the result of a spontaneous conformational change in the native prion protein. It occurs at random in about 1 to 2 people per million of the population per year and accounts for 85%–90% of all cases of prion disease. sCJD mainly affects, people in the 50–70 year age group. The length of the illness can vary but sporadic CJD is often recognised for its rapid progression, with survival usually only 3–6 months, however, exceptions do occur in the age of onset, symptoms and the duration of illness.
Genetic CJD and other forms of inherited prion diseases
Genetic forms of prion disease, depending on the country, usually accounts for only 10 – 15% of cases of CJD. Other forms of inherited human prion disease are Gerstmann-Sträussler Scheinker Syndrome (GSS) and Fatal Familial Insomnia (FFI).
- Familial CJD (fCJD)
- Gerstmann Sträussler Scheinker Disease (GSS)
- Fatal Familial Insomnia (FFI)
Genetic forms of CJD are often recognised from a family history of the illness in two or more first degree blood relatives and a patient’s DNA can be tested for a mutation of the prion protein gene (PRNP), however, very often there is no family history of similar illness in the proband and the patient may be the first person within a family found to have a mutation in their PRNP.
In genetic forms of CJD, there is a mutation in the prion protein gene that is typically inherited in families in an autosomal dominant fashion, meaning that from generation to generation approximately 50% of family members will carry the mutation and develop CJD ie in general each person carrying the genetic mutation has a 50% chance of passing it onto each of their children. Someone carrying the gene will most likely develop the illness in their lifetime, however, there is no test to know when, or if they will live long enough to actually become symptomatic.
Most forms of genetic CJD are impossible to differentiate from sporadic CJD and it is not until a gene test is done that a genetic cause can be established. In contrast to Familial CJD (fCJD), patients with GSS often survive for several years and patients with FFI typically suffer from a progressive and untreatable form of insomnia.
Aquired forms of prion disease
Iatrogenic CJD (iCJD)
Although rare this is an acquired form of the disease associated with transmission via medical treatments and surgical procedures. In the mid 1970s it became evident that CJD could be transmitted from one person to another through invasive medical procedures including cornea transplants or contaminated surgical instruments. In the 1980s it was recognised that explanted material, such as human pituitary hormones, for fertility and short stature, dura mater grafts and corneal transplants, accidentally contaminated with prion protein, could also transmit this disease to recipients.
There is also a recognised risk of transmission from the use of contaminated surgical instruments used on ‘at risk patients’ for procedures involving high infectivity tissues such as brain, spinal cord and the posterior part of the eye.
Refer page 4 of CJD Infection Control Guidelines (pdf)
A prion disease affecting the Fore people of Papua New Guinea, was instrumental in establishing that CJD is transmissible. In the 1960’s it was realised that Kuru was transmitted through cannibalism.
From the Kuru experience in Papua New Guinea we have also learnt that incubation periods of prion disease can be longer than 50 years, and this may be dependent on our genetic makeup and the type of prion disease. There is the possibility of two different types of amino acids at codon 129 of the prion protein gene–methionine (M) or valine (V). As everyone has two copies of the gene, people can be MM, MV or VV, with 47% of the caucasian population being MV. All of the patients with primary acquired vCJD, with one possible exception have been MM which indicates to researchers that genotype appears to influence the susceptibility of prion disease transmission.
Kuru: The Science and the Sorcery (Youtube)
Variant CJD (vCJD)
Variant CJD (vCJD) was first reported in 1996 following the first death of an affected individual in 1994 in the UK. There have been about 229 cases, mainly in the UK, as a result of the consumption of BSE contaminated products and it is now known that vCJD can be transmitted through blood and blood products. Variant CJD is typically quite different from CJD in that it has a longer duration of illness-approximately 14 months, often presents with psychiatric and sensory symptoms and affects a much younger age group (median age at death 28 years). Abnormal forms of the prion protein are often found in peripheral tissues such the spleen, lymph nodes and tonsils and pose extra risks of transmission that do not occur in CJD . The examination of the vCJD brain shows widespread deposits of abnormal prion protein, called florid plaques. This form of plaque is not seen in sCJD.
Variant CJD is often incorrectly referred to as ‘Mad Cow Disease’ by the media and has subsequently been used inappropriately by healthcare professionals.
The incidence of vCJD is declining in those affected countries but there is fear that there may be another delayed wave of vCJD amongst VV and MV genotype people due to the longer incubation periods for these genotype groups as suggested by previous experience with acquired forms of prion disease.
BSE has NOT been found in Australian livestock and to date there have been no reported cases of vCJD in Australia.
How Australia will respond to our first case of vCJD- A guide for the public (pdf)
This pdf document is a guide to show Australians how the Australian Government will respond to this event and to outline measures already undertaken to protect the Australian public from vCJD.
We wish to thank the department of Health and Ageing for the provision of this article.