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As long as i remember from my biology class (mutation) 

⇒ specific facial characteristics e.g. upward slanting eyes, small folded ears, a small mouth giving the appearance of a large tongue, a small flattened nose and a short wide neck. 
⇒ poor muscle tone making them appear floppy, as babies.
⇒ a single crease that goes directly across the palm of the hand.
⇒ intellectual disability
⇒ heart defects