Finally, several primary immunodeficiency syndromes, including X-linked lymphoproliferative disease (XLP) type I due to hemizygous mutation of SH2D1Agene, OMIM *300490), and type II due to mutation of BIRC4/XIAP gene (OMIM *300079) are associated with a high risk of developing HLH [18], [19]. This evidence concerns the gene XIAP and X-linked lymphoproliferative disease.