Nightshade Vegetables and reactions/effects?

Has anyone heard of the nightshade vegetables. I've been researching a condition my wife has, as she has always had really bad allergies etc, and now this. Came across info about these.
What I found it that these vegetable (ie. white potatoes, tomatoes, peppers, etc) have small traces of the nightshade poison, and some people have reactions to them that can present in different areas of their bodies or bodily systems. Most people don't have any problem with them but possibly those with heightened allergies may. I don't know.

I just wanted to reach out and see what real world experience, from real people, there is about these. It just blew my mind when I read about it and wondering how common this is to have reactions to them.

Thanks.