STORY HIGHLIGHTS

• Actor Michael J. Fox says he has good days and bad days
• Fox says he’s "pretty sure" he has Parkinson’s, although there’s no blood test or imaging study
• Fox’s foundation has raised $200 million for Parkinson’s research

Editor’s note: "Sanjay Gupta MD Reports: a Conversation with Michael J. Fox" airs at 6 p.m. ET Friday on CNN. a version of this story was originally published on September 29.

(CNN) — when I went to Michael J. Fox’s neighborhood this morning, I had no idea what time we would start our interview. "he has to time his medications," I was told. "when his medications kick in, he will be ready." As far as I could tell, Fox’s medications kicked in right away, and for the next 90 minutes, we talked about everything.

Fox spoke about the hard shoes he has to wear first thing in the morning, because his feet and legs are so stiff. he humorously added that he just puts his toothbrush in his mouth and lets the movement of his head do the rest of the work. As a neurosurgeon, it was fascinating to hear Fox describe his brain surgery with such great clarity and his fears about doing it again. "Well, it is brain surgery…," he said with flourish.

There is a lot we don’t know about Parkinson’s disease. for starters, no one is sure what causes it. One’s genetics likely loads the gun, and something in the environment pulls the trigger. but what?

It might surprise you to know four people on the set of Fox’s first television series, "Leo and Me," developed early onset Parkinson’s disease. a statistical anomaly, or a clue? Fox and his foundation’s scientists aren’t sure. The actor paused when I asked him about it, he shrugged his shoulders and said, "I am not as concerned about a few people. I am focused on everyone who has the disease."

And, to that end, he is putting the $200 million his foundation has raised to work. You won’t hear as much about stem cells from Fox or the foundation, but he will describe in detail the efforts of a five-year, international biomarker study his foundation is funding. The goal is to find more clues about the disease, by collecting samples from patients. it is true that most therapies simply mask the symptoms, and Fox said he believes that if they find new targets of the disease, it will greatly accelerate the treatments available.

I asked Fox if he was even sure he had Parkinson’s disease. after all, there is no blood test or imaging study. it is just a clinical diagnosis, and Fox’s condition was diagnosed at age 30. he has officially had the disease for nearly two decades. Fox told me he’s pretty sure he has it, but even today Parkinson’s disease is not an exact science.

Fox looked very good this day. he told me he has good days and bad days.

People think of the natural state of Parkinson’s as the symptoms of stiffness, tremor and lack of facial expression. when Fox is medicated, it is different. he is smiling, passionate and has constant, fluid movements, instead of rigidity.

"Those are the dyskinesias," he told me. "but it buys me time to do the things I want to do," he added with a characteristic grin.