What's going on in the brain? I understand the bad actor in this is dopamine. Maybe you can help us understand what that is. And also I understand oven with Parkinson's and these other symptoms you mention can be depression.
Yes. So to address the first, the dopamine, there's an area in the brain, deep in the brain, called the substantia nigra. And that area makes a chemical called dopamine. And dopamine then talks to other cells and tells them what to do. And, again, for reasons that we don't understand those cells that make the dopamine start to degenerate. And so that's where a lot of the problems come because the pathways that that chemical is involved in are the pathways that mediate movement, and so that's why we see many of the signs that is we see.
We now recognize as well that there are probably other chemicals that are involved as well. So before we used to talk only about what we called the motor symptoms of Parkinson's disease, movement and things like that. Now we recognize that there are nonmotor symptoms. So one of those would be depression. Other things you can see are things like sleeping problems, urinary frequency, constipation, a multitude of other things that we call nonmotor symptoms. And some of that's probably because it's not just the dopamine that gets affected but there are other chemicals that can be affected as well.
In terms of depression, depression is actually very, very common in Parkinson's disease. About 40 percent of patients with Parkinson's disease do have depression. And it's higher in Parkinson's disease than you see in other illnesses of the chronic type. So when you compare patients who have other chronic illnesses to those with Parkinson's disease there is a much higher incidence of depression in Parkinson's.
And, again, part of that is a reactive thing. Right, it's understandable. You've now got a disease. It's affecting the way you can do things. You're allowed to be depressed. But it goes beyond that, and part of that is that the chemicals that are involved, one of them being dopamine, is affected, and that's why there is a higher instance.
Now, is Parkinson's always progressive? And if it is always progressive how do you look at Patient A or Patient B and know how rapidly it will progress?
Yes. Parkinson's disease by its definition is a progressive disorder. It's a neurodegenerative condition, so it does continue to progress. It progresses very slowly, so we always tell patients with Parkinson's disease if something happens overnight or you snap your fingers and the next thing there's been an acute change, that's not Parkinson's disease. Something is going on, and we need to look for that something else. It is quite variable, the rate of change from person to person, but in general it does change slowly over months or years as opposed to weeks or days.