1. Laboratory of Biochemical Genetics and Metabolism, The Rockefeller University, New York, New York 10021, Laboratory of Lipoprotein Research, Cardiovascular Institute and Department of Medicine, Mount Sinai School of Medicine, New York, New York 10029, Department of Medicine, College of Physicians and Surgeons, Columbia University, New York, New York 10032, and Department of Biochemistry, MCP·Hahnemann School of Medicine, Philadelphia, Pennsylvania 19129