Fear of the progressive disease may have fed the comedian’s depression, but Parkinson’s can also cause depression and anxiety.

Robin Williams was experiencing the early stages of Parkinson’s disease before his death Monday, his widow, graphic designer Susan Schneider, disclosed today.

“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,” Schneider said in a press statement.

In addition to tremors and shaky movements, Parkinson’s can also cause cognitive decline and mood disorders, including depression and anxiety. In some cases, those symptoms begin before the hallmark physical symptoms do. Half of Parkinson’s patients suffer from clinical depression at some point during the course of their disease.

Schneider’s statement suggests that fear of the disease’s progressive toll fed Williams’ existing depression.

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“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,” she said.

The causes of Parkinson’s disease are still unknown, but its effects on the brain have been well documented. The progressive illness causes neurons to die, and as they do, patients produce less of the neurotransmitter chemical dopamine. This lack of dopamine leaves them unable to move normally. It may also spur mental decline.

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Ironically, in the 1990 film “Awakenings,” Williams starred as a fictional representation of a British neurologist named Oliver Sacks who in the late 1960s treated patients paralyzed from encephalitis with L-dopa, a drug that spurs the production of dopamine and is sometimes used to treat Parkinson’s. The form of encephalitis featured in the film can cause movement disorders similar to those seen in Parkinson’s patients.

Yesterday, Michael J. Fox, an actor who also suffers form Parkinson’s, announced his foundation’s work with Intel to develop a smart watch-based mobile app to monitor the movements of Parkinson’s patients. The app will provide doctors with better data on how the disease progresses in each individual.

Sixty thousand Americans are diagnosed with Parkinson’s disease each year.

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Photo courtesy of Wikimedia Commons, Paul Hudson.