<<Disclaimer:  Verify this information before applying it to your situation.>>

MSG can indeed cause a serious reaction, and lurks in many seemingly
non-grain foods, such as tuna fish and tomato paste.  Watch out for
Contadina tomato paste, it contains "hydrolyzed vegetable protein"
which I believe is the same as MSG, and can be formulated from wheat. I
made the mistake of using it in chili, and my celiac husband had a
reaction.  We couldn't figure it out until I went back and read the
label.