mission of bovine spongiform encephalopathy,  also called “mad cow disease.” Typically,
individuals with CJD present with neurocognitive deficits , ataxia, and abnormal move-
ments such as myoclonus, chorea, or dystonia; a startle reflex is also common. Typically,
the history reveals rapid progression to major NCD over as little as 6 months, and thus the
disorder is typically seen only at the major le vel. However, many individuals with the dis-
order may have atypical presentations, and the disease can be confirmed only by biopsy or
at autopsy. Individuals with variant CJD may present with a greater preponderance of
psychiatric symptoms, characterized a by lo w mood, withdrawal, and anxiety. Prion dis-
ease is typically not diagnosed without at le ast one of the characteristic biomarker fea-
tures: recognized lesions on magnetic resonance imaging with DWI (diffusion-weighted
imaging) or FLAIR (flu id-attenuated inversion recovery), tau or 14-3-3 protein in cerebro-
spinal fluid, characteristic triphasic waves on electroencephalogram, or, for rare familial
forms, family history or genetic testing. 
Prevalence
The annual incidence of sporadic CJD is a pproximately one or two cases per million peo-
ple. Prevalence is unknown but ve ry low given the short survival.
Development and Course
Prion disease may develop at any age in adults—the peak age for the sporadic CJD is ap-
proximately 67 years—although it has been report ed to occur in individuals spanning the
teenage years to late life. Prodromal symptoms  of prion disease may include fatigue, anx-
iety, problems with appetite or sleeping, or difficulties with concentration. After several