TTN and systemic lupus erythematosus: Of the remaining genes, five are autoantigens: complement component receptor 1 (CR1) in SLE and multiple sclerosis (MS); pepsinogen 4, group I (PGA4) in pernicious anemia (PA); titin (TTN) in myasthenia gravis (MG); interferon-gamma-inducible protein 16 (IFI16) in RA, SLE, SSc and SJ; and HP in celiac disease (CEL) (Table 1).