Flow cytometric assessment of LDL receptor activity peripheral blood mononuclear cells compared to gene mutation detection in diagnosis of heterozygous familial hypercholesterolemia

Background: Studies indicate that human peripheral blood mononuclear cells mirror low-density lipoprotein (LDL) receptor activity of other cells in th e body. To measure LDL receptor activity in patients with heterozygous fami lial hypercholesterolemia (FK), we prepared peripheral blood mononuclear ce lls from individuals with molecularly verified LDL receptor defective (Trp( 66)-Gly mutation, n = 18) or receptor negative (Trp(23)-stop mutation, n = 17) heterozygous FH and from healthy individuals (n = 24). Methods: The cells were stimulated to express maximum LDL receptor by prein cubation in lipoprotein-free medium. They were then incubated at 4 degrees or 37 degrees C with fluorescently conjugated LDL (DiI-LDL), T-lymphocytes and monocytes were identified by fluorescently conjugated monoclonal antibo dies. DiI-LDL bound (at 4 degrees C) or internalized (at 37 degrees C) by t he cells was measured using flow cytometry. Knowing the LDL receptor gene m utation of the FH patients allowed us to compare the diagnostic capability of our functional assay with the DNA diagnosis. Results: The diagnostic accuracy did not allow our assay to be used for dia gnosis of individual cases of heterozygous FH. Conclusions: We suggest that our two-color fluorescence flow cytometry assa y can be used to characterize functionally gene mutations causing LDL recep tor dysfunction in patients with heterozygous FH. Cytometry 36:52-59, 1999, (C) 1999 Wiley-Liss, Inc.