Primary deficiencies of natural killer cells are rare conditions associated with defective cellular immunity.
Criteria for NKD - all of the following:
(1) stable over time
(2) one of the following types of NK cell deficiencies
(2a) absence of NK cells (classical NKD), with <= 1% of peripheral blood lymphocytes
(2b) presence of NK cells but with defective cell activity (functional NKD)
(3) exclusion of secondary cause (drug, malignancy, infectious)
(4) not due to a defect in natural killer T cells (T cells that express certain NK cell surface determinants)
Functional evaluation:
(1) reliable and validated assay, such as 51Cr-release cytotoxicity assay using K562 target cells)
(2) defective >= 3 occasions separated by one month
Additional features:
(1) Patients with NKD are susceptible to certain infections which may be the presenting event.
(2) Other family members may be affected.
(3) Identification of a mutation in a gene associated with NKD.
