Cause of US student's 'extensive' brain damage a mystery after North Korea release

An US college student who emerged from prison in North Korea in a coma has severe brain damage but doctors do not know what caused it, a team treating him has said.

The doctors described Otto Warmbier, 22, as being in a state of "unresponsive wakefulness" but declined to discuss his outlook for improvement, saying such information would be kept confidential.