No definitive cause has been determined and doctors have generally concluded that they were born with it.

In each case, a definitive cause has never been found.

The subsequent investigation did not find a definitive cause to the accident.

No definitive cause has been found for the illnesses among the villagers.

"We do not have a definitive cause of the problem," he said.

There has yet to be a theory put forward that is widely accepted as a true definitive cause.

The definitive cause of the accident has never been determined.

"At this point, we don't have any definitive cause for the illness," she said.

But he said Cuban health officials were seeking a more definitive cause.

As of 11 November 2010, a definitive cause for the failure had not been determined.