Predisposition to autoimmune diseases in patients with decreased function of the Fas antigen, is multifactorial and may involve factors controlling lymphocyte responsiveness, autoantigen expression and immune effector functions, and may include defects in several levels: in the Fas antigen, in the interaction between Fas and FasLigand or defects of co-stimulatory pathways of B or T cells [2]. Here, FAS is linked to autoimmune disease.