Prions are the infectious agents responsible for several neurodegenerative diseases in mammals. This happens due to the abnormal folding of the proteins in the brain. It refers to the hypothesis that the infectious agents causing the diseases contain only proteins. It explained why infectious agents are resistant to ultraviolet radiation. They can break down the nucleic acids but are receptive to substances that denature proteins.
Structure of Prions
Prions are found all over the body but the ones that cause diseases are structurally different. Few of them are even resistant to proteases. The two isoforms of prions are:
- PrPc: These prion proteins are found on the cell membrane and play an important role in cell signaling and cell adhesion. More research is being carried out to discover its functions.
- PrPsc: This is the disease-causing prion and is resistant to proteases. It affects the confirmation of PrPc and changes it. They are believed to have more beta sheets than alpha-helices. It also forms highly structured amyloid fibers. The other free proteins also attach to the end of these fibers. Similar prions with similar amino acids can only bind. However, cross-species binding is also possible but is very rare.
Types of Prion Diseases
Prion diseases can be of three types- acquired, sporadic, or genetic.
- Acquired Prion Disease: The acquired prion diseases occur when a person is exposed to an infectious protein. Though scary, these prions are rarely caught by the people. For eg., in kuru diseases, the prions were transmitted to people by cannibalism. Its main source was New Guinea pig.
- Genetic Prion Disease: Familial prion diseases are caused as a result of genetic transmissions. However, it is not necessarily inherited from the ancestors. It may be caused due to a mutation in some DNA.
- Sporadic Prion Disease: Prion diseases are also believed to be sporadic. This means that its cause is not confirmed. This form of prion disease is the most common to date.
Symptoms of Prion Disease
Prion disease has a long incubation period, often years. However, when symptoms develop, they worsen progressively and at times rapidly. Some of the common symptoms of this illness are:
- Personality changes are the arrival of agitation, depression, etc.
- Rapidly developing dementia
- Uncontrolled muscle spasms
- Losing coordination
- Difficulty in speaking