Genetic causes comprise the apoptotic Fas-FasL pathway components (FAS, FASL, FADD, CASP10 and CASP8), being germinal and somatic mutations in FAS gene (ALPS-FAS and ALPS-sFAS, respectively) the most common cause of ALPS (60% and 15%, respectively) (7, 8, 10–14). This evidence concerns the gene FAS and autoimmune lymphoproliferative syndrome.