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: Psychiatry
Second most common cause of chromosomal abnormality causing mental retardation - 
Select and explain. 
A. Down's syndrome, B. Fragile X syndrome, C. Edward syndrome, D. Patau syndrome
B: Fragile X syndrome
Answer: B: Fragile X syndrome 
Explanation: "Fragile X syndrome is the second most common genetic cause of mental retardation, after Down syndrome".