Thank you for your brief look into the relation of HLA-B27 to MG. Yes it is more relating to AS (ankylosing spondylitis) which I also have thus my piqued interest. There is a stronger relation of MG to HLA-B8, however in late onset of MG in Males (age 60-80) there is an association with HLA-B27.

http://eyewiki.aao.org/Myasthenia_Gravis

"The disease has a bimodal pattern, having an early peak in the second and third decade, and a late peak in the sixth to eighth decade. The early peak shows a female predominance, approximately 3:1, and an association with HLA-B8, HLA-DR3, and HLA-DR1, the latter being more specific for ocular MG. Interestingly, the late peak features a male predominance and an association with HLA-B27 and HLA-DR2"

This is another good link to the dysfunction of the T cell and the genetic link to MG:
http://europepmc.org/backend/ptpmcre...8&blobtype=pdf