GFAP and rheumatoid arthritis: Approximately 20% of patients with GFAP-A also have autoimmune diseases such as type 1 diabetes, autoimmune thyroid disease, and rheumatoid arthritis.[4] Some patients may have a combination of other positive antibodies, most commonly NMDA, AQP4, and MOG, and we have reported patients who did not show positive results for these antibodies.