Robin Williams shocked the world earlier this year when he committed suicide, and many were left with the questions that surround the sudden death of any famous person; in particular, “Why did he do it?” Although Williams had been known to suffer from depression, his fans and friends wondered if there might have been another factor at work, and now, an autopsy report shows that the comedian suffered from a little-known disorder.

Known as Lewy body disease, the disorder is similar to Parkinson’s and affects the memory and speech centers. It can also cause hallucinations before it develops into dementia. Unfortunately, the symptoms of both diseases are so similar that often, doctors misdiagnose them and prescribe the wrong medication, which can make things worse for the patient.

“Even experienced neurologists have trouble distinguishing between (the two diseases). There’s not a clear-cut distinction. It’s two diseases that have a kind of intersection where it’s hard to tease them apart,” said neurologist Gayatri Devi.

Devi, who did not treat Williams, said that suicide is unusual for patients suffering from Lewy body disease, but TMZ reported this week that a source close to his family admitted that the disorder may have played a role in his choosing to take his own life.

Williams reportedly left the majority of his $50 million estate to his three children, with his wife Susan taken care of under the terms of their pre-nuptial agreement.