ALP phenotype B (ALP-B), characterized by a predominance of small, dense LDL particles as determined by gradient gel electrophoresis, has been associated with increased risk of myocardial infarction and a constellation of atherogenic lipid and apolipoprotein (apo) changes. Based on complex segregation analysis, ALP-B appeared to be influenced by a single major genetic locus with a dominant mode of inheritance and a common allele frequency. This project was designed to identify a new gene involved in susceptibility to coronary heart disease.