Final answer:
The abnormality of PrPSc compared to PrPC lies in its misfolded conformation, usually caused by a somatic mutation or the presence of an existing rogue prion, which can then lead to transmissible spongiform encephalopathies.
Step-by-step explanation:
After no size or post-translational differences were found between PrPC and PrPSc, the factor that could make PrPSc abnormal is its misfolded conformation. Prion proteins, such as PrPC, are normally found in healthy brain tissue and are involved in various cellular processes. However, when a PrPC is misfolded into the rogue form PrPSc, due to reasons such as a somatic mutation or interaction with an existing PrPSc, it adopts a structure rich in β-pleated sheets which is resistant to proteolysis. This newly misfolded protein can induce other normal prion proteins to also misfold, leading to a chain reaction resulting in the formation of amyloid plaques and eventually, neurodegenerative diseases known as transmissible spongiform encephalopathies (TSEs).