This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Medicine
A chromosomal anomaly associated with Alzheimer's dementia is: 
Select and explain. 
A. Trisomy 18, B. Patau syndrome, C. Trisomy 21, D. Turners syndrome
C: Trisomy 21
Answer: C: Trisomy 21 
Explanation: Answer is C (Trisomy 21) : Several genetic factors are known to play impoant roles in pathogenesis of at least some cases of Alzheimers disease. Trisomy 21 is one of them. Adults with trisomy 21 (Down's) consistently develop the Neuropathologic hallmark's of Alzheimer's disease if they survive beyond age 40.