Types of Prion Diseases

Our introduction to prion diseases this week, like the mad cow disease and scrapie, got me interested in reading more about prion diseases. Usually we classify diseases into four categories: genetic, degenerative, infectious or bacterial/viral. However, it was interesting to note that prion can be classified as sporadic, genetic and acquired. All differ with relation to signs, symptoms and duration of the disease.
There are two types of sporadic diseases (Creutzfeldt-Jakob Disease (sCJD) and Sporadic Fatal Insomnia (sFI)), which means that they occur in people without any known risk factors or gene mutations. The typical symptoms for sCJD include imbalance and incoordination, memory loss and impaired thinking, and psychiatric symptoms such as anxiety or depression. Once the symptoms do appear, CJD progresses very quickly and is usually fatal within a few months of symptom onset. sCJD typically affects people in their 60s and is rarely seen in people younger than 40 years old.
For the genetic strain of the disease, this is caused by inherited mutations in the prion protein gene (PRNP) which provides instructions to your cells regarding how to make prion protein. In the genetic form, the mutations cause the cells to form an abnormal prion protein instead of the normal one. This could be passed down through generations or could be a new mutation in the gene. The symptoms of this largely depend on the type of the mutation but include: balance & coordination problems, memory loss and impaired thinking.
Prion protein diseases can also be caused by exposure to prion, however, this is extremely rare and acquired diseases account for only 1% of the prion protein cases. This could be contracted through either exposure to these prion proteins in certain types of medical settings or the ingestion on beef or any other meat affected by this condition. In the early symptoms patients often present with personality changes and psychiatric symptoms such as depression or withdrawal. Physical symptoms start developing a little later such as falling, difficulty walking, stumbling etc. The estimated incubation period is 5-40 years and the durations of the illness is typically 12-24 months after signs and symptoms appear.
Therefore, even for this one specific disease, it is extremely interesting how there are many different ways of contracting it.