A rapidly progressive, fatal, degenerative disease in humans caused by an abnormal PRION protein. There are three aetiological forms of CJD: sporadic, IATROGENIC, and inherited. Sporadic CJD occurs randomly in all countries and has an annual incidence of one per million. Iatrogenic CJD is caused by accidental exposure to human prions through medical and surgical procedures (and cannibalism in the case of the human prion disease known as kuru that occurs in a tribe in New Guinea, where it is called the trembling disease). Inherited or familial CJD accounts for 15 per cent of human prion disease and is caused by a MUTATION in the prion protein gene. In recent years a new variant of CJD has been identiﬁed that is caused by BOVINE SPONGIFORM ENCEPHALOPATHY (BSE), called variant CJD. The incubation period for the acquired varieties ranges from four years to 40 years, with an average of 10–15 years. The symptoms of CJD are dementia, seizures, focal signs in the central nervous system, MYOCLONUS, and visual disturbances.
Abnormal prion proteins accumulate in the brain and the spinal cord, damaging neurones (see NEURON(E)) and producing small cavities. Diagnosis can be made by tonsil (see TONSILS) biopsy, although work is under way to develop a diagnostic blood test. Abnormal prion proteins are unusually resistant to inactivation by chemicals, heat, X-RAYS or ULTRAVIOLET RAYS (UVR). They are resistant to cellular degradation and can convert normal prion proteins into abnormal forms. Human prion diseases, along with scrapie in sheep and BSE in cattle, belong to a group of disorders known as transmissible spongiform encephalopathies. Abnormal prion proteins can transfer from one animal species to another, and variant CJD has occurred as a result of consumption of meat from cattle infected with BSE.
From 1995 to 1999, a scientiﬁc study of tonsils and appendixes removed at operation suggested that the prevalence of prion carriage may be as high as 120 per million. It is not known what percentage of these might go on to develop disease.
One precaution is that, since 2003, all surgical instruments used in brain biopsies have had to be quarantined and disposable instruments are now used in tonsillectomy.
Measures have also been introduced to reduce the risk of transmission of CJD from transfusion of blood products.
In the past, CJD has also been acquired from intramuscular injections of human cadaveric pituitary-derived growth hormone and corneal transplantation.
The most common form of CJD remains the sporadic variety, although the eventual incidence of variant CJD may not be known for many years.