UNC13D and hemophagocytic syndrome: There are five subtypes of FHL: FHL type 1 is unknown in gene and its chromosomal location; FHL type 2 includes perforin gene (perforin 1 [PRF1], located at 10q21-22) mutation; FHL type 3 has the Munc 13-4 gene (unc-13 homolog D (UNC13D), located at 17q25) mutation; FHL type 4 includes mutations in STX11 (located at 6q24); and FHL type 5 has Munc 18-2 gene (syntaxin binding protein 2 [STXBP2], located at 19p13) mutation.