LOS ANGELES — Robin Williams was in the early stages of Parkinson’s disease at the time of his death, 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 died Monday in his Northern California home. Authorities said he committed suicide.

“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.

Schneider did not offer details on when the actor comedian had been diagnosed or on his symptoms.

The Marin County Sheriff’s Department, which said Williams hanged himself, is conducting toxicology tests and interviews before issuing a final ruling. Lt. Keith Boyd of the Marin County Sheriff’s Department did not return phone calls and email messages from The Associated Press seeking comment on Schneider’s statement.

Williams’s 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 and is known for his efforts to fund research into it, tweeted that he was stunned to learn Williams had early symptoms.

“Stunned to learn Robin had PD. Pretty sure his support for our Fdn predated his diagnosis. A true friend; I wish him peace,” Fox tweeted.

This Nov. 23, 2009 photo released by Starpix shows actor-comedian Robin Williams performing his stand-up show, “Weapons of Self Destruction,” at Town Hall in New York. Williams' wife Susan Schneider released a statement Thursday, Aug. 14, 2014 announcing that Williams had early stages of Parkinson's disease. He died Monday of an apparent suicide at the age of 63. (photo credit: AP Photo/Starpix, Dave Allocca)

Actor-comedian Robin Williams performing his stand-up show, ‘Weapons of Self Destruction,’ at Town Hall in New York, on November 23, 2009. (photo credit: AP/Starpix, Dave Allocca)

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.

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.

It’s important to emphasize that not everyone who is depressed has Parkinson’s or is likely to develop it, she added, especially given “this tragic case” involving Williams in which the two diseases occurred.

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.

Dr. Christopher Gomez, neurology chairman at the University of Chicago, said while it makes sense to think that a diagnosis could make someone feel depressed, depression and Parkinson’s have a deeper, more organic connection. They are thought to affect the same regions of the brain, although their neurological relationship isn’t well understood, he said.

“It’s downright curious that there’s so much depression in Parkinson’s,” Gomez said.

Williams had publicly acknowledged periodic struggles with substance abuse, including alcohol. Recently, depression prompted him to enter rehab.

Schneider said that those who loved Williams are taking solace in the outpouring of affection and admiration for him.

“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 in her statement.

Williams, whose comic brilliance first gained wide attention in the 1980s sitcom “Mork & Mindy,” evolved into a respected dramatic actor who starred in films such as “Good Will Hunting,” for which he won an Oscar, “Dead Poets Society” and “Mrs. Doubtfire.”

He was invariably upbeat in public and with his friends and colleagues, and was known for his philanthropic efforts and support for US troops and veterans.

Over the years, Williams had described himself as an “honorary Jew” and in many of his skits channeled a stereotypical elderly Jewish lady, or alternatively, a New York rabbi. The legendary performer also played several Jewish, or at least Jewish-inspired, characters, most notably Tommy Wilhelm, in a cinematic adaptation of Saul Bellow’s “Seize the Day.”

Recently, Williams posted a picture on Twitter showing him with a white yarmulke on his head while on the set of the CBS TV show “The Crazy Ones.”

“Too late for a career change?” he wrote. “Rabbi Robin.”

From his breakthrough in the late 1970s as the alien in the hit TV comedy “Mork & Mindy,” through his standup comedy act and such films as “Good Morning, Vietnam,” the short, barrel-chested Williams ranted and shouted as if just sprung from solitary confinement. Loud, fast and manic, he parodied everyone from John Wayne to Keith Richards, impersonating a Russian immigrant as easily as a pack of Nazi attack dogs.

He was a riot in drag in “Mrs. Doubtfire,” or as a cartoon genie in “Aladdin.” He won his Academy Award in a rare dramatic role, as an empathetic therapist in the 1997 film “Good Will Hunting.”

He was no less on fire in interviews. During a 1989 chat with The Associated Press, he could barely stay seated in his hotel room, or even mention the film he was supposed to promote, as he free-associated about comedy and the cosmos.

“There’s an Ice Age coming,” he said. “But the good news is there’ll be daiquiris for everyone and the Ice Capades will be everywhere. The lobster will keep for at least 100 years, that’s the good news. The Swanson dinners will last a whole millennium. The bad news is the house will basically be in Arkansas.”

Like so many funnymen, Williams had dramatic ambitions. He played for tears in “Awakenings,” ”Dead Poets Society” and “What Dreams May Come,” which led New York Times critic Stephen Holden to write that he dreaded seeing the actor’s “Humpty Dumpty grin and crinkly moist eyes.”

But other critics approved, and Williams won three Golden Globes, for “Good Morning, Vietnam,” ”Mrs. Doubtfire” and “The Fisher King.”

His other film credits included Robert Altman’s “Popeye” (a box office bomb), Paul Mazursky’s “Moscow on the Hudson,” Steven Spielberg’s “Hook” and Woody Allen’s “Deconstructing Harry.” On stage, Williams joined fellow comedian Steve Martin in a 1988 Broadway revival of “Waiting for Godot.”

“Robin was a lightning storm of comic genius and our laughter was the thunder that sustained him. He was a pal and I can’t believe he’s gone,” Spielberg said.

In addition to his wife, Williams is survived by his three children: daughter Zelda, 25; and sons Zachary, 31; and Cody, 19.