STXBP2 and hemophagocytic syndrome: Biallelic mutations inUNC13D (encoding Munc13-4, accounting for about one third of FHL cases),STX11 (encoding syntaxin 11, about 5% of FHL cases), andSTXBP2 (encoding syntaxin-binding protein 2, also known as Munc18-2, about 20% of FHL cases) led to the occurrence of HLH in FHL types 3, 4, and 5, respectively26–29.