Increased levels of Body Mass Index (BMI) are associated with increased mortality and morbidity from cardiovascular disease, hypertension, diabetes and other disorders. The recent dramatic increase in obesity in the American population has reached epidemic proportions, with two-thirds of the general population meeting criteria for "over-weight" and one-third meeting criteria for "obese". While the increase in the prevalence of obesity reflects changing lifestyle and dietary habits, genetic factors are shown to influence the susceptibility for obesity. Animal and human studies reveal that a high-calorie/high fat-diet produces substantial differences in weight gain on different genetic backgrounds. Understanding the genes that influence susceptibility to obesity will permit investigation into treatment to prevent or reduce weight gain and reverse the population trend for increasing obesity. The NHLBI Family Heart Study (FHS) found compelling linkage for BMI (LOD = 4.9) on chromosome 7q31-q34. This region has been implicated in at least sixteen other genome scans for obesity and related traits, and may be the most widely replicated locus in obesity genetics. We believe the FHS sample to be the largest study of the region and to provide the best opportunity to identify the implicated genes. This group of investigators has worked extensively with the FHS, the Framingham Study, and the Family Blood Pressure Program Project, and has performed genome scans in these large study samples. The 4.9 LOD for BMI to chromosome 7q31-q34 is the largest reported for any trait in these studies. Yet genome scans have little value if they are not followed by gene discovery. We suggest that this application offers a unique opportunity to fulfill the purpose of those scans. Over the past 2 years and 2 months we have genotyped 421 SNPs in the 7q31-q34 region, and SNP linkage in our focus sample generates a LOD = 16 for BMI. We will show compelling evidence for a haplotype in the 5' region of the Leptin gene (p<0.00005) influencing BMI among men in our sample. We will further demonstrate that the responsible gene in this region is not Leptin. SNP and haplotype association studies implicate three strong candidate loci and other loci also warrant additional study. We propose to confirm SNP association in an independent study of 200 families showing linkage to the same position (from Dr. R. Arlen Price's group). Those loci with confirmed association will be further characterized by sequencing, genotyping new polymorphisms, and gene expression studies to identify the responsible genes. The proposed studies offer a unique opportunity to discover important BMI related genes at 7q31.