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Creutzfeldt-Jakob disease (CJD) is a rare and fatal neurodegenerative condition. It is named after the two doctors who, between 1920 and 1921, recognized the first cases (although they are now considered quite atypical). The disease is classified as a transmissible spongiform encephalopathy due to the characteristic appearance of brain tissues in the affected patients. Different forms of the disease are currently recognized.

 

The most common form (accounting for about 85% of cases) is known as sporadic CJD. It usually affects adults over 50 years of age, but its cause is still unclear. Symptoms typically include rapidly progressing dementia, associated with a characteristic electroencephalogram (EEG) pattern. In the brain tissue, the disease causes lesions (“holes”, hence the name spongiform) accompanied by amyloid plaques, i.e. accumulations of specific proteins.

 

The new variant

Arguably the most talked-about form of CJD, new variant Creutzfeldt-Jakob disease (nvCJD) is linked to the consumption of contaminated beef products and was first identified in 1996. The first cases appeared in the United Kingdom in the mid-1990s. Unlike sporadic CJD, this variant typically affects younger adults (aged 15 to 50 years) and the mean survival time is approximately 15 months. The incubation period is still unclear, but several studies suggest that it may range from 4 to 40 years. Affected people present with sensory disturbances, severe pain, memory loss, involuntary movements, ultimately progressing to dementia, mutism, immobility and death. Compared to sporadic CJD, the brain lesions are more widespread, amyloid plaques appear elongated and surrounded by more of the holes characteristic of the spongiform structure. In addition, in this form of CJD, the pathological protein tends to accumulate not only in the brain, but also in lymphatic tissue, including the tonsils. Right from the start, all these findings led researchers to believe that nvCJD was indeed a new type of encephalopathy. Further features include characteristic EEG features and the presence of a specific protein (fragment 14-3-3) in the cerebrospinal fluid.

 

Familial CJD

Beside the sporadic form and the new variant, three familial forms of the disease have been recognized that are associated with specific mutations in the gene coding for the prion protein (PrP). This means that members of the same family are more likely to contract the disease. In particular, the onset of familial CJD (fCJD) is typically at an earlier age than the sporadic form.

 

Gerstmann-Sträussler-Scheinker disease (GSS) is another inherited condition associated with mutations in the PrP gene, and is characterized by involuntary movements and dementia. The duration of the disease ranges from 2 to 10 years.

 

Also included among hereditary spongiform encephalopathies is fatal familial insomnia (FFI), another rare inherited condition associated with a mutation in the PrP gene and characterized by insomnia and central nervous system disturbances.

 

Iatrogenic CJD

Some forms of CJD result from exposure to contaminated material. In particular, iatrogenic CJD occurs when the infection is accidentally spread during medical procedures involving contaminated biological material or surgical instruments that have not been properly decontaminated. Several causes were identified in the 1970s, including corneal transplantation, use of contaminated neurosurgical instruments and depth electrodes. In 1985, iatrogenic CJD was first reported in patients who had received growth hormone extracted from dead bodies. In Italy, most of the cases occur after neurosurgery, especially dura mater grafting, dura mater being the membrane surrounding the brain.

 

Kuru

Until a few decades ago, Kuru caused countless deaths in Papua New Guinea. This disease affects the central nervous system and is invariably fatal. Research carried out by Carleton Gajdusek in the 1950s made it possible to link the spread of the disease, apparently confined to Papua New Guinea, to funerary rituals during which indigenous peoples consumed the brains of their deceased family members. Therefore, foodborne transmission presumably occurred by ingestion of contaminated flesh.

Publication date: 2 January 2021