Question

Which of the following statements is NOT true about prion disease?

• A. About 10% of patients have myoclonus
• B. It is caused by an infectious protein
• C. Dementia is a universal feature
• D. Brain biopsy is diagnostic

Hint:

Myoclonus is far more common than 10% in prion disease, and dementia, though typical, is not seen in every case or every prion disease.

Answer 1

The Correct Option is A, C

Step 1: Go through each option as a separate true/false test.
The question wants the option(s) that do NOT hold for prion disease, so each choice needs to be checked against what is actually known about conditions like CJD.

Step 2: Test the infectious protein claim.
Prion disease is unique because the infectious agent is a misfolded protein (PrPSc) with no genetic material at all. It works by forcing normal PrP to refold into the abnormal shape. This matches known biology, so this option holds up as true.

Step 3: Test the myoclonus number.
Clinical studies of CJD report myoclonus in a majority of patients as the disease advances, generally cited near 80 to 90%, far above 10%. A figure of only 10% is too low, so this option fails the test.

Step 4: Test the "universal dementia" claim.
Dementia is a core and common feature of CJD, but "universal" is a strong word meaning every single case, every single prion disease. Because some prion diseases and atypical presentations can start with ataxia, insomnia, or psychiatric change without dementia being the presenting or invariable feature, this option also fails the test.

Step 5: Test the brain biopsy claim.
A brain biopsy can show the spongiform vacuolation typical of prion disease and is accepted as a diagnostic method, so this option holds up as true.

Step 6: Collect the failing options.
Two statements do not hold: the 10% myoclonus figure and the claim that dementia is universal.
\[ \boxed{\text{10\% have myoclonus AND dementia is universal (both NOT true)}} \]