Prions

What are Prions?

The term Prion means proteinaceous infectious particles. Prions are the infectious agents responsible for several neurodegenerative diseases in mammals, like, Creutzfeldt Jakob disease. 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 the infectious agents are resistant to ultraviolet radiations. They can break down the nucleic acids, but are receptive to substances that denature proteins.

Also read: Communicable and Non-Communicable Diseases

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 signalling 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 the alpha helices.

It also forms highly structured amyloid fibres. The other free proteins also attach to the end of these fibres. Similar prions with similar amino acids can only bind. However, cross-species binding is also possible, but is very rare.

Diseases Caused by Prions

Prions are quite rare and difficult to transmit. But they are progressive neurodegenerative diseases with no cure or treatment. These diseases develop gradually.

These proteins affect many other animals in addition to humans. For eg., scrapie in sheep, mad cow disease in cows, chronic wasting disease in deer. The prion diseases in humans are Creutzfeldt-Jakob disease, Fatal Familial Insomnia, kuru disease, etc.

Prions can spread in a person’s brain for years without any symptoms. The prions start killing neurons and the symptoms strike the brain in no time. Soon the person’s health starts declining.

All the prion diseases are fatal, some last a few months, and some might last for years. A few experimental pieces of evidence show that the prions are not ordinary infectious materials. It is believed to be a “self-replicating protein”.

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 the 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

The 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 the 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 most common to date.

Causes of Prion Diseases

The main cause of prion diseases is the abnormal folding and clumping of prions in the brain causing brain damage. This leads to memory impairment, changes in the personality, difficulties in moving.

Prions are by far the most dangerous infections caused by the agents already present within the body and are usually fatal. However, a lot has not been discovered about prion diseases.

Risk Factors Involved

People with genetic history related to prion disease are at risk of Prion disease.

Eating meat infected by “mad cow disease” increases the risk of Prion disease.

Contaminated medical equipment or contaminated corneas can cause Prion disease.

Symptoms of Prion Disease

Following are the symptoms of Prion diseases:

• Developing dementia

• Hallucinations

• Fatigue

• Stiffening of muscles

• Confusion

• Difficulty in speaking

Also read: Infectious diseases

Discovering the mechanism of replication of prions has been a very difficult task. To find out how can a protein multiply without any cellular machinery was next to impossible. But this is what prions do. There are many other concepts related to prions that are unclear. Researches are being carried out to figure out the in and outs of prions for detailed studies.

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