XIAP and hemophagocytic syndrome: Primary HLH, also known as familial HLH (FHL), is caused by a deficiency of specific genes, namely, perforin1 (PRF1), UNC13D, syntaxin 11 (STX11), syntaxin binding protein 2 (STXBP2), lysosomal trafficking regulator (LYST), RAB27A, AP3B1, SH2D1A and X-linked inhibitor of apoptosis (XIAP) as well as some other unknown genes [1–5].