20/20: My Extreme Affliction (3)

Profiles of a former Washington Redskins cheerleader who suffered from a mysterious neurological disorder, and British "brainman" Daniel Tammet, who learned Icelandic in seven days; a report on Williams syndrome, a rare genetic disorder with an unusual side effect (people with it often have sunny dispositions). Also: Tourette's syndrome in children is explored in video diaries made at a summer camp in Upstate New York for kids who have the disorder.

Source: ABC