Hope he gets the help he needs. Found this article about bipolar disease if interested in learning more about the causes
Author: Mood Disorders Association of BC Bipolar disorder is a brain disorder that results in extreme changes of mood, energy and ability to function. Although research has improved our understanding of why someone might develop bipolar disorder, the exact cause is still not known.
www.heretohelp.bc.ca
This paragraph says it all:
"Scientists believe that bipolar disorder is the result of a
complicated relationship between genetic and environmental factors. Research suggests that a person is born with a "vulnerability" to bipolar illness, which means that they are more prone to developing the disorder. However, this is not the only factor in determining whether a person will become ill. Environmental factors
such as stressful life events also appear to play a role in that they can lead to the onset of the illness or "trigger" a relapse of symptoms."
Since he's potentially genetically predisposed, when you add what the family has gone through to his own particular issues, this almost sounds inevitable. Let's hope he gets the help he needs.