NK-cell and CTL CD107a assays identify most patients with genetic disorders of degranulation. Results of CD107a degranulation assays using resting NK cells (A-C), IL-2–activated NK cells (D-F), or short-term CTL blasts (G-H) from patients with FHL3 (A,D,G), FHL4 (B,E), or FHL5 (C,F,H). ΔCD107a (%) indicates the difference in the percentage of cells expressing CD107a before stimulation subtracted from the percentage of cells expressing CD107a after stimulation; ΔCD107a (MFI), respective difference in MFI; Pr. 1, protocol 1; and Pr. 2, protocol 2. The gray shaded areas represent the range from the 10th to the 90th percentile of values obtained in healthy donors. Closed symbols represent patients manifesting with HLH before age 2; open symbols indicate manifestation of HLH after age 2.