FCGR2A and Guillain-Barre syndrome: Therefore, our systematic review with meta-analysis assesses and reports a structured, transparent summary of the current knowledge of FCGR2A (rs1801274) and FCGR3A (rs396991) polymorphisms in autoimmune diseases [immune thrombocytopenia (ITP), systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), Guillain-Barré syndrome (GBS), celiac disease (CD)].