Sự kết hợp chính xác và mức độ nghiêm trọng của các triệu chứng này thay đổi rộng rãi giữa các trường hợp và các loại bệnh prion. CJD, phổ biến nhất của bệnh prion con người, được đặc trưng bởi sự suy giảm nhanh chóng trong chức năng tâm thần từ sự nhầm lẫn và mất trí nhớ | diminished appetitie and fatigue may occur prior to the onset of the more serious symptoms. The exact combination and severity of these symptoms varies widely between cases and types of prion disease. CJD the most common of the human prion diseases is characterized by a rapid deterioration in mental function from confusion and memory loss into severe dementia accompanied by loss of muscular control ataxia and twitching or spasmodic motion myoclonus . Other symptoms include vision and speech impairment. A scan of electrical activity in the brain called an electroencephalogram EEG will often show an abnormal periodic spike pattern. The onset of symptoms usually occurs when the patient is over age 50 and death follows within one to five years. Microsopic holes or vacuoles in the brain tissue which give it a spongiform appearance are characteristic of CJD. Gertsmann-Straussler-Scheinker syndrome GSS encompasses a variety of disorders. One form of the disease the ataxic form is first characterized by an unsteady walk sometimes accompanied by leg pains. These motor problems get worse over several years and are finally accompanied by mental and behavioral breakdown. By contrast dementia is the main characteristic of the telencephalic form of GSS accompanied by rigidity the inability to make facial expressions tremors and stuttering or stammering. In another form of the disease GSS with neurofibrillary tangles the main features are loss of muscle coordination ataxia tremors and progressive insanity. As in CJD the affected individuals are usually in their fifties or older and the progression of the disease may take from two to six years. The most noticeable sign of fatal familial insomnia FFI is the untreatable and progressively worse difficulty in sleeping. The affected individual then begins to experience complex hallucinations which are often enacted dreams. Excessive sweating irregular heartbeat high blood pressure and hyperventilation are other symptoms. Motor .
