There exists indisputable evidence about the participation of MHC in autoimmune diseases. Reiter disease and ankylosing spondilytis have been related to HLA-B27; while in psoriasis vulgar it has been proposed B13, B17, and B37 represent risk factors. Class II genes, in addition to RA, such as DR2 and DR3 are linked to Takayasu’s Arteritis and systemic lupus eritematous. Multiple sclerosis by contrast, is believed to be associated with DR2. There is also evidence that Type I Diabetes and Pemphigus vulgaris have DR4 as a participant allele (Garavito 2003), so it would be desirable to exclude a possible participation of patients with these antecedents during a genetic survey for RA.