Caspase-8 is the most upstream protease of the activation cascade of caspases responsible for the TNFRSF6/FAS mediated and TNFRSF1A induced cell death. Caspase-8 forms an aggregate with FADD called death-inducing signaling comple, Xenopus/Amphibian, (DISC). DISC performs caspase-8 proteolytic activation. The active dimeric enzyme is liberated from the DISC and free to activate downstream apoptotic proteases. Defects in caspase-8 are the cause of caspase-8 deficiency (CASP8D). CASP8D is a disorder resembling autoimmune lymphoproliferative syndrome (ALPS). It is characterized by lymphadenopathy, splenomegaly, and defective CD95-induced apoptosis of peripheral blood lymphocytes (PBLs).