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
All of the following may occur in Down's syndrome, except: 
Select and explain. 
A. Hypothyroidism, B. Undescended testis, C. Ventricular septal defect, D. Brushfield's spots
B: Undescended testis
Answer: B: Undescended testis 
Explanation: Undescended testis has not been described as an association with Down's syndrome. Hypothyroidism, ventricular septal defect, Brushfield's spots are seen in Down's syndrome. Ref: Essential Pediatrics By O P Ghai, 6th Edition, Page 592; Down Syndrome By Mark Selikowitz, 2008, Preview.