Thuja, do you know if the monoclonal IgG in your MGUS is specific for SGPG?

This should be easy to establish; purify some of the monoclonal IgG from your serum and then run it against SGPG in an immunoassay - maybe in an ELISA, maybe in an immunoblot.

If that turns out to be the case (doing the experiment is the only way to find out) then more aggressive treatment of your MGUS may be indicated.

Your health care team should be able to help with this.