In previous works, we correlated certain variants of the perforin gene (PRF1) with ALPS/DALD development and suggested that mild heterozygous variations of PRF1 incapable of inducing FHL may act as susceptibility genes for ALPS/DALD development in subjects displaying defective Fas function [21,22]. This evidence concerns the gene FAS and Dianzani autoimmune lymphoproliferative disease.