When I had consult with my surgeon he mentioned hearing about another newly discovered MG implicated anti-body, but couldn't remember what it was called or if there was a test for it yet. Today I found an article from Nov 2013. Won't let me post a link here for it since I'm fairly new to the board, but here's the title if you want to search for it on*edit*

Research Uncovers New Cause for Muscle-Weakening Disease Myasthenia Gravis

Will be bringing a copy of the full journal article (link to that is in the posted article) into my next appointment with my neurologist to find out what he knows about it. If I have a supportive medical team that's not questioning the diagnosis in spite of being seronegative for AChR and MuSK, is it worth it to do another test just for curiosity sake (assuming a test is/becomes available)?

LRP4 antibody tests are not readily available, so far as I am aware.

I guess each of these tests is expensive, so it is no surprise that, with a rare disease if 80% are AChR positive 10% MuSK positive and some smaller percentage maybe LRP4 positive, then the rarer the version you have the more costly the tests will get.

If you have a medical team accepting that you are seronegative MG, the only reason that an extra test would be worthwhile would be if that particular version of MG responded to different treatments.