Robin Williams was in the early stages of Parkinson's disease and was sober at the time of his suicide, his wife said Thursday.
In a statement, Susan Schneider said that Williams, 63, was struggling with depression, anxiety and the Parkinson's diagnosis when he was found dead Monday in his Northern California home.
Schneider did not offer details on when the actor comedian had been diagnosed or his symptoms.
Williams' death shocked fans and friends alike, despite his candor about decades of struggle with substance abuse and mental health. With Parkinson's, Williams faced shouldering yet another challenge.
Parkinson's disease is an incurable nervous system disorder that involves a loss of brain cells controlling movement. Tremors, sometimes starting out in just one hand, are among the early symptoms.
It can also cause rigid, halting walking, slowed speech and sometimes dementia. Symptoms worsen over time and can often be treated with drugs.
Actor Michael J. Fox, who has long had the disease, is known for his efforts to fund research into it. Pop star Linda Ronstadt revealed in 2013 that she had Parkinson's and said the disease had robbed her of her ability to sing. Boxer Muhammad Ali, the late radio personality Casey Kasem and the late Pope John Paul II are among other well-known figures diagnosed with the disease.
"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.
Parkinson's affects about 1 million people nationwide, 6 million globally. The cause isn't known but genes are thought to play a role.
There is no standard test for Parkinson's; doctors rely on symptoms, medical history and neurological exams to make the diagnosis.
Dr. Tanya Simuni, director of the Parkinson's Disease and Movement Disorders Center at Northwestern University's medical school in Chicago, said patients often react to the diagnosis with surprise and despair.
Depression is often present even in early stages and can sometimes precede tremors that help doctors make the diagnosis, Simuni said.
Referring to Williams, she said it's important to emphasize that not everyone who is depressed is at risk for Parkinson's, "especially in this tragic case."
She noted that many can live for years without severely debilitating symptoms, but also that 20 years after diagnosis, as many as 80 percent develop dementia. Antidepressants are among drugs commonly prescribed for the disease, along with medication to help control jerky movements.