Robin Williams' suicide was caused by a terrible disease called Lewy Body Dementia, sources close to his family told TMZ. They believe it was the "key factor" that prompted him to take his own life.

TMZ has obtained documents that state that Williams was stricken with the disease in which abnormal protein deposits in the brain disrupt normal brain function. In addition, the tabloid site was told that Williams' doctors agrees that Lewy Body Dementia was the critical factor resulting in his suicide.

Lewy Body Dementia is commonly associated with Parkinson's disease. It affects an estimated 1.3 million people in the U.S. While it differs from Parkinson's, both diseases cause biological changes in the brain. Over time, afflicted people develop cognitive, behavioral, sleep and physical symptoms.

People afflicted by Lewy Body Dementia are treated with medications that can cause severe side effects. Patients report seeing hallucinations, like people or animals.

Williams' wife told authorities following his death that he often complained about how the medications made him feel.

Williams was found hanging from a belt at his home in Marin County, California, on Aug. 11. His cause of death was suicide by asphyxia. He was 63.

The comedian suffered from depression, emotional distress, suicidal tendencies and substance abuse for years, but these personal struggles did not diminish his vibrant performances on stage and screen. He started his career as a stand-up comedian performing in San Francisco and Los Angeles in the mid-1970s, and later achieved fame as Mork in the television series "Mork & Mindy."

During his acting career, Williams had acclaimed performances in many movies, including "Dead Poets Society," "Good Will Hunting," "The Birdcage," "Mrs. Doubtfire" and "Jumanji."

Williams has left his $50 million estate to his three children Zachary, 31, Zelda, 25, and Cody, 22, in the form of a trust, and his wife will be financially cared for under the terms of a prenup, reports MailOnline.

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