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
Not a feature of Hartnup's disease 
Select and explain. 
A. Cerebellar ataxia, B. Cutaneous photosensitivity, C. Mental retardation, D. Psychological disturbance
C: Mental retardation
Answer: C: Mental retardation 
Explanation: In hartnup's disease, mental development is normal.