Robin Williams was in the early stages of Parkinson's Disease — but was not ready to share that information publicly — when he took his own life, his wife said Thursday in a statement, adding that he died with his sobriety "intact."

Parkinson's is a degenerative central nervous system disorder that causes tremors, stiffness and slowing of movement over time. Severe depression — for which Williams had been seeking treatment — is one of the disease's most common psychiatric symptoms.

SEE ALSO: Robin Williams Has 4 New Films Coming, None Left Unfinished

Michael J. Fox and Muhammad Ali both suffer from Parkinson's, which can be controlled to varying degrees by medication.

The entire statement, from Susan Schneider:

Robin spent so much of his life helping others. Whether he was entertaining millions on stage, film or television, our troops on the frontlines, or comforting a sick child — Robin wanted us to laugh and to feel less afraid. Since his passing, all of us who loved Robin have found some solace in the tremendous outpouring of affection and admiration for him from the millions of people whose lives he touched. His greatest legacy, besides his three children, is the joy and happiness he offered to others, particularly to those fighting personal battles. Robin's sobriety was intact and he was brave as he struggled with his own battles of depression, anxiety as well as early stages of Parkinson's Disease, which he was not yet ready to share publicly. It is our hope in the wake of Robin's tragic passing, that others will find the strength to seek the care and support they need to treat whatever battles they are facing so they may feel less afraid.

The revelation in part helps explain why someone as vibrant, beloved and successful as Williams would choose to take his own life. It also essentially completes the profile of a group whose risk for suicide has spiked alarmingly in recent years: Middle-aged white men at the end of a successful career who have a history of chronic depression, substance abuse — and a serious medical condition.

Williams was open about his lifelong struggles with addiction, and checked in last month for a tune-up after a relapse that began in 2006. But the only known medial issue he had involved an aortic valve replacement in 2009.

The suicide rate for aging white males with the aforementioned characteristics jumped by nearly 40 percent from 1999 to 2010, according to Centers for Disease Control statistics cited in a Washington Post article published Tuesday.