FLOW-CYTOMETRY WITH A MONOCLONAL-ANTIBODY TO THE LOW-DENSITY-LIPOPROTEIN RECEPTOR COMPARED WITH GENE MUTATION DETECTION IN DIAGNOSIS OF HETEROZYGOUS FAMILIAL HYPERCHOLESTEROLEMIA

We used a fluorescence flow cytometry assay with a monoclonal low dens ity lipoprotein (LDL) receptor-specific antibody to detect LDL recepto r expression on blood T lymphocytes and monocytes. We prepared periphe ral blood mononuclear cells from patients with genetically verified LD L receptor-defective (Trp(66)-Gly mutation, n = 17) or receptor-negati ve (Trp(23)-stop mutation, n = 17) heterozygous familial hypercholeste rolemia (FH) and from healthy individuals (n = 24). The cells were sti mulated to express the maximum amount of LDL receptor by preincubation in lipoprotein-deficient medium. A dual-labeling technique allowed fl ow cytometric analysis of LDL receptor expression on cells identified by fluorescently conjugated surface marker antibodies. Knowing the LDL receptor gene mutation of the FH patients allowed us to compare the d iagnostic capability of this functional assay with the DNA diagnosis a nd to validate the assay with molecular genetics instead of clinical i ndices of heterozygous FH. T lymphocytes expressed more LDL receptors and gave better diagnostic results than monocytes, and cells from pati ents with either the Trp(66)-Gly or the Trp(23)-stop mutation had vari able but significantly reduced LDL receptor expression. The data indic ate that this fluorescence flow cytometry assay is unsuitable for diag nosis of individual cases of heterozygous FH but that it may be useful for functionally characterizing mutations in the LDL receptor gene.