This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Miscellaneous, Subject name: Medicine
Triplet repeat is seen in all EXCEPT 
Select and explain. 
A. Fragile-x syndrome, B. Huntington's disease, C. Friedreich's ataxia, D. Cystic fibrosis
D: Cystic fibrosis
Answer: D: Cystic fibrosis 
Explanation: (D) Cystic fibrosis