ApoE deficiency: markedly decreased levels of cellular ApoE mRNA

Apolipoprotein (apo) E deficiency is a rare genetic disease characterized by palmar and tuberoeruptive xanthomas, type III hyperlipoproteinemia, and premature atherosclerotic vascular disease. The plasma level of apoE in apoE deficiency is less than 0.05 mg/dl by radioimmunoassay, and no structural variants of apoE were detected by immunoblot of plasma or VLDL separated by two-dimensional gel electrophoresis. The apoE gene is present in the apoE deficient patient, and there are no major insertions or deletions in the gene by Southern blot analysis. Blood monocyte-macrophages isolated from a patient with apoE deficiency contain 1-3% of the level of apoE mRNA present in monocyte-macrophages isolated from normal subjects. The apoE mRNA in the monocyte-macrophages of the apoE deficient patient is similar in size to normal apoE mRNA. The deficiency of plasma apoE in the patient with apoE deficiency is due to a markedly decreased level of apoE mRNA and decreased production of the E apolipoprotein. The decreased apoE mRNA may be due to a defect in transcription or processing of the primary transcript of the apoE gene or to instability of the apoE mRNA. The decreased plasma level of apoE results in delayed clearance of remnants of triglyceride rich lipoproteins, hyperlipidemia, and a type III phenotype.