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: Pathology
True about fragile-X syndrome - 
Select and explain. 
A. Triple nucleotide repeat sequence, B. Chromosome breaking, C. Mitochondrial mutation, D. Centrachrome absent
A: Triple nucleotide repeat sequence
Answer: A: Triple nucleotide repeat sequence 
Explanation: Ans. is 'a' i.e., Triple nucleotide repeat sequence Trinucleotide-repeat mutations disorders Expansion affecting coding regions Expansion affecting non-coding regions o Spinobulbar muscular atrophy (Kennedy disease) o Fragile-X syndrome o Huntington disease o Freidreich ataxia o Dentatorubral-pallidaluysion atrophy (Haw river syndrome) o Myotonic dystrophy o Spinocerebellar ataxia