All of the following may occur in Down's syndrome, except:
Hypothyroidism
Undescended testis
Ventricular septal defect
Brushfield's spots
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.