NK-cell frequencies in the peripheral blood of control individuals, NPC1 patients, and carrier parents. (A-D) NK cells were identified using a CD45+ lymphocyte gate and defined as CD16/56+CD3− using a clinical whole-blood TBNK monitoring assay. (A,C) NK-cell frequency as a percentage of CD45+ lymphocytes is depicted. (B,D) Absolute numbers of NK cells per microliter of blood is depicted. For all panels, each symbol indicates an individual sample with the line at the median. (A-B) *P < .05, **P < .01, and ***P < .001 calculated by a Mann-Whitney U test using GraphPad Prism v4. Circles represent control NPC1+/+, diamonds represent NPC1+/− carriers, and squares represent affected NPC1−/− blood samples. (C-D) Correlation lines were calculated by the Spearman method with the following R values: (C) control 0.3356 and NPC1 0.0523, (D) control 0.1698 and NPC1 −0.1661. het, heterozygous carriers.