Although the other ALPS forms (due to FADD (79), CASP8, or CASP10 deficiency) have not yet been studied by flow cytometry due to the unavailability of specific fluorescent conjugated antibodies, mutations in the FAS receptor is the most frequent disease form of ALPS found in ~70% of genetically defined ALPS (177, 178) thereby making flow cytometry an essential screening tool for patients suspected to have ALPS. Here, FADD is linked to autoimmune lymphoproliferative syndrome.