ALPS patients on average present with a 10-fold increase in DN T cell proportion (Bleesing et al., 2001a; Bristeau-Leprince et al., 2008; Magerus-Chatinet et al., 2009) and a sizeable proportion of DN T cells can also be found in the lymphoid organs of the murine models for ALPS, namely lpr/lpr (Fas-deficient) and gld/gld (FasL-deficient) mice (Cohen and Eisenberg, 1992; Watanabe-Fukunaga et al., 1992; Takahashi et al., 1994). Here, FAS is linked to autoimmune lymphoproliferative syndrome.