PRF1 and hemophagocytic syndrome: FHLdb (https://www.biotoclin.org/FHLdb) is a comprehensive collection of reported variants in the 4 genes known to cause FHL: PRF1, UNC13D, STXBP2, and STX11. The literature search yielded 433 different variants in these genes, distributed as follows: 240 missense, 69 frameshift, 51 nonsense, 51 splicing, 10 in-frame indel, 7 deep intronic, and 5 large rearrangements (Figure 1).