A Texas woman was diagnosed with a rare medical condition called Foreign Accent Syndrome (FAS) after waking up from surgery with a British accent, in spite of being born and raised in Rosenberg, Texas. The woman underwent Orthognathic surgery (overbite) that led to a nerve damage which has her speaking like a cockney. 

This rare condition is often caused by brain damage from a stroke, but it's also been linked to multiple sclerosis among other issues. 

It is a subject of lively debate about how such a condition would be welcomed if it meant speaking with an American or British inflection.