Abstract: Using methods of comparative and functional genomics, a new gene coding for apolipoprotein A5 was identified in the vicinity of APOA1/C3/A4 cluster on human chromosome 11q23 by Pennaccio team and Vliet team. The open reading frame of human APOA5 encoded a 366-amino acid protein with high sequence homology to mouse Apoa5 and human APOA4. Mice expressing a human APOA5 transgene showed a decrease in plasma triglyceride concentrations to one-third of those in control mice; conversely, knockout mice lacking Apoa5 had four times as much plasma triglycerides as controls. Single nucleotide polymorphisms (SNPs) in APOA5 (S19W, –1131T>C) and APOA5 haplotype (APOA5*3) were independently associated with high plasma triglyceride levels. These findings indicate that APOA5 is an important determinant of plasma triglyceride levels, a major risk factor for coronary artery disease.