Myasthenia gravis, like other autoimmune diseases, is a complex disease and a combination of different factors appear to contribute to its development, including environmental factors, smoking history, sex hormones, and exposure to certain viruses. Studies of identical twins have shown that some people have genetic risk factors that predispose them to acquiring the disease. Individuals with certain versions (alleles) of HLA genes are more likely to develop the disease. HLA genes encode proteins that present ‘antigens’ or foreign objects on the surface of cells, which are recognized by cells of the immune system (T cells) (Beisswanger 2007). Scientists discovered associations between the presence of certain HLA alleles and early-onset myasthenia gravis, late-onset myasthenia gravis, and thymic abnormalities. Other gene alleles have also been shown to be associated with myasthenia gravis, including PTPN22, CHRNA1, and CTLA-4 (Zagoriti 2013). It is hoped that by identifying possible genetic risk factors for myasthenia gravis, more effective treatment options or preventive therapies can be discovered.