CJD is caused by a protein known as a prion. Infectious prions are misfolded proteins that can cause normally folded proteins to become misfolded. About 85% of cases occur for unknown reasons, while about 7.5% of cases are inherited from a person's parents in an autosomal dominant manner. Exposure to brain or spinal tissue from an infected person may also result in spread. There is no evidence that it can spread between people via normal contact or blood transfusions. Diagnosis involves ruling out other potential causes. An electroencephalogram, spinal tap, or magnetic resonance imaging may support the diagnosis.