This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Genetics, Subject name: Pathology
Which of the following is not caused by over expression of a trinucleotide repeat? 
Select and explain. 
A. Alzheimer's disease, B. Fragile X, C. Huntington disease, D. Spinocerebellar ataxia Type 2
A: Alzheimer's disease
Answer: A: Alzheimer's disease 
Explanation: Ans: a (Alzheimer's disease) Ref: Ganong, 22nd ed, p. 215Alzheimer's disease is not caused by over expression of a trinucleotide repeat. The rest 3 options are examples of trinucleotide repeat diseases where as Alzheimer's is primarly a degenerative disease (Basal ganglia) resulting in movement disorder.Some examples of trinucleotide repeat diseases:-Huntington's disease -- CAGSpinocerebellar ataxia --CAG(Type 1, 2, 3, 63)Fragile X syndrome -- CGGMyotonic dystrophy -- CTGFrederich's ataxia -- GAA