This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: NEET 2019, Subject name: Pathology
Which of the following is true about Fragile X syndrome? 
Select and explain. 
A. Triple nucleotide CAG Sequence mutation, B. 10% female carriers are mental disability, C. Affected males have IQ of 20-40, D. Micro-orchidism in affected males
C: Affected males have IQ of 20-40
Answer: C: Affected males have IQ of 20-40 
Explanation: Fragile X syndrome Long repeating sequence of three nucleotides. 2nd most common genetic cause of mental retardation after Down syndrome. It is caused by a trinucleotide mutation in the familial mental retardation-1 (FMR1) gene (CGG Repeat). Affected males are mentally retarded, with an IQ in the range of 20 to 60. Characteristic physical phenotype -Large mandible, large eveed ears, and large testicles (macro-orchidism). The most distinctive feature is macro-orchidism in at least 90% of affected post pubeal males. Thiy percent to 50% of carrier females are affected (i.e., have intellectual disability. etc.)