LOS ANGELES — 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.