Robin Williams was sober and in the early stages of Parkinson's disease when he committed suicide earlier this week, his widow said Thursday.

Williams, who authorities said appeared to have hanged himself with a belt and cut his wrist , was suffering the early symptoms of the neurological disease.

"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," his widow, Susan Schneider, said in a statement yesterday.

For years, Williams struggled with alcohol and drug addiction, most recently checking himself in to a Minnesota facility in July.

However Schneider said Williams had recently been coping with depression and anxiety, but his "sobriety was intact" before is death.

News of the diagnosis shed some light Williams' recent struggle with depression, a common early manifestation of the neurological disease, said Dr. Miran Salgado, director of the Center for Parkinson's Disease and Movement Disorders at New York Methodist Hospital.

Many patients can experience depression 10 to 12 years before any motor symptoms manifest, Salgado said.

"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," Schneider said Thursday. "His greatest legacy, besides his three children, is the joy and happiness he offered to others, particularly to those fighting personal battles."

Williams, who was 63, was not yet ready to share his Parkinson's diagnosis with the public, she said.

Williams was discovered by his assistant on Monday with a belt wrapped around his neck, wedged between a closed closet door and door frame, said Lt. Keith Boyd, assistant chief deputy coroner with the Marin County Sheriff's Office.

Schneider was the last person to see Williams alive before she went to bed at about 10:30 p.m. on Sunday, Boyd said. Williams then went into another bedroom inside the Tiburon home, just north of San Francisco.

Parkinson's disease is the result of the loss of dopamine-producing brain cells, which manifests itself in tremors; rigidity; postural instability; and bradykinesia, or slowness of movement, according to the National Institute of Neurological Disorders and Stroke.

Genetics as well as certain toxins are known to cause the disease, Salgado said.

Early symptoms are subtle and occur gradually, according to the institute. There is no cure, but symptoms can be managed through medication or surgery.

"For five to six years you can live with it without anyone noticing," Salgado said. "You can mask it by taking medications."

Clinical depression is the No. 1 factor that impacts Parkinson's patients, said Joyce Oberdorf, president and CEO of the National Parkinson Foundation.

"There is a chemical basis to it in Parkinson's," she said. "Dopamine is a feel good chemical. You're low in dopamine so you don't feel so well, emotionally."

For someone in the public eye, Oberdorf said, it can be very hard to come to terms with the diagnosis.

"The first few years for someone with Parkinson's tends to be much more emotional -- the symptoms tend to be slight," she said. "It's really dealing with the emotional impact of 'who should I tell?' It could be a lot of anxiety about what the future could hold.

"It's very very common to conceal it," she added.

Actor Michael J. Fox, 53, has famously struggled with the disease for years and founded a rerearch foundation into the disease bearing his name.

"Stunned to learn Robin had PD," Fox wrote on his verified Twitter account Thursday. "Pretty sure his support for our Fdn predated his diagnosis. A true friend; I wish him peace."

Fox was diagnosed with young-onset Parkinson's disease in 1991, but waited 7 years to publicly admit it.