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: Pediatrics
Which is not true about Fragile X syndrome ? 
Select and explain. 
A. Large testis, B. Pigmented nevi, C. Large ear present, D. No large nose
B: Pigmented nevi
Answer: B: Pigmented nevi 
Explanation: Ans. is 'b' i.e., Pigmented nevi Fragile - X syndrome Fragile - X syndrome is the prototype of diseases in which the mutation is characterized by a long repeating sequence of three nucleotides. o In fragile X syndrome,trinucleotide repeat mutation involve CGG on non coding region. o Clinical features of fragile - X syndrome Mental retardation Long face with large mandible Hyperexntesible joint Mitral valve prolapse Large eveed ears Large testis (macro-orchidism) High arched palate o Fragile X syndrome is the second most common cause of mental retardation, after Downs syndrome.