Tia Stroke Causes?

Hello all! My brother is 38 years old and when he was asleep two nights back he had a transient ischaemic attack. We called the doctor early morning and he said that it was a mild attack. When I spoke to him yesterday he told me that he felt really weak on that night, his brain was not focussing on anything, he was having trouble in concentrating. Thereafter he felt a sharp pain arising from his arm which made him unconscious. I want to know all possible Tia stroke causes?