Using genetically engineered mice to understand apolipoprotein-B deficiency syndromes in humans

Several human diseases are characterized by defects in the synthesis and secretion of the apolipoprotein (apo) B-containing lipoproteins. Familial hypobetalipoproteinemia is caused by mutations in the apo-B gene and is characterized by abnormally low plasma concentrations of apo-B and low-density lipoprotein (LDL) cholesterol. Another apo-B deficiency syndrome, abetalipoproteinemia, is caused by mutations in the gene for microsomal triglyceride transfer protein (MTP). MTP is a microsomal protein that is thought to transfer lipids to the apo-B protein as it is translated, allowing it to attain the proper conformation for lipoprotein assembly. A third apo-B deficiency syndrome, Anderson's disease (or chylomicron retention disease), is characterized by the inability to secrete apo-B-containing chylomicrons from the intestine but an apparently normal capacity to secrete lipoproteins from the liver. To more fully understand these human apo-B deficiency syndromes, our laboratory has generated and characterized gene-targeted mouse models. This review summarizes what has been learned from these animal models.