IMPROVED DETECTION OF FAMILIAL HYPERCHOLESTEROLEMIA BY DETERMINING LOW-DENSITY-LIPOPROTEIN RECEPTOR EXPRESSION IN MITOGEN-INDUCED PROLIFERATING LYMPHOCYTES

In view of the presence of some 190 mutations in the low density lipop rotein receptor (LDLR) gene and a lack of simple detection methods, we have developed an improved assay system for detecting familial hyperc holesterolemia (FH) using mitogen-induced proliferating lymphocytes, F reshly isolated mononuclear cells were cultured for 3 days in RPMI 164 0 supplemented with 10% human lipoprotein-deficient serum (LPDS) and 1 % phytohemagglutinin (PHA), LDLR expression was measured by how cytome try using a monoclonal anti-LDL-R antibody or DiI-LDL, Mitogenic respo nses were monitored by cell size (FSC), interleukin-2 receptor (IL2-R) expression, and stimulation index (SI), The LDL-R expression in PHA-s timulated lymphocytes was significantly higher than lymphocytes or mon ocytes cultured without PHA (15.2- and 3.6-fold, respectively). The gr adation of the LDL-R expression was highly correlated to FSC, IL2-R ex pression, and SI (r > 0.9 in each case). However, no difference in FSC , IL2-R expression, or SI existed between 30 clinically diagnosed FH a nd 42 normolipemic control subjects. The significantly lower LDL-R exp ression in the FH group (45.2 +/- 15.3% versus 100 +/- 14.1%; unpaired t test, P < 0.0001) indicated the presence of genetic defects. Normoc holesterolemic first degree relatives and non-FH hypercholesterolemic subjects demonstrated normal LDL-R expression as did the controls. The assay carries an efficiency of 97% and both sensitivity and specifici ty of 98.5%. Measurement of low density lipoprotein receptor expressio n in phytohemagglutinin- and lipoprotein-deficient serum-stimulated ly mphocytes offers a simple method for detecting familial hypercholester olemia with improved sensitivity.