Functional characterization of two low density lipoprotein receptor gene mutations by fluorescence flow cytometric assessment of receptor activity in stimulated human T-lymphocytes

We report a functional characterization of the W23X and W66G low density lipoprotein (LDL) receptor gene mutations. The authors used two-color fluorescence flow cytometry to measure LDL receptor activity in stimulated T-lymphocytes, prepared from patients heterozygous for the W23X or W66G mutation, and compared the results with measurements of LDL receptor activity in stimulated T-lymphocytes prepared from unrelated healthy control subjects. It was found that the W23X mutation significantly reduced LDL receptor expression and LDL binding and internalization, and that the W66G mutation significantly reduced LDL receptor expression and LDL binding. LDL internalization in patients heterozygous for the W66G mutation was not significantly reduced. The data support the concepts that the W23X mutation prevents production of LDL receptors (class I) and that the W66G mutation produces LDL receptors unable to recycle normally in cells (class V).