system
Given the following post, respond as if you're commenting on Reddit:
human
Why are prions only found in the brain?

Fairly self explanatory... I need some clarification.
gpt
In short, they are not. Prions are misfolded, aberrant proteins. These "buggy" proteins (not specifically prions) are found in all cells in all organisms. Prions (there are many types of them)  are unique because they can cause other similar proteins to become aberrant, and therefore are considered to be "infectious" (the name prion is derived from the words protein and infection). The brain is especially susceptible because the blood brain barrier stops these proteins from leaving as waste.