Several twin and adoption studies as well as animal models have confirmed that obesity has a strong genetic component. It is apparent that obesity in humans has a complex polygenic background; that is, the phenotype is determined by an unknown number of genes together with environmental factors. However, there may well be single genes playing a major role within certain families, but the gene may vary from family to family. Two interesting gene candidates have been found in mouse experiments, the ob and the db gene, the products of which are probably a satiety hormone and its receptor, respectively, which regulate food intake. The recent cloning of the ob gene and its human homologue constitute a major breakthrough in this field. The 16-kD protein encoded by the ob gene is called leptin, and is well conserved among vertebrate species. The pig could be a valuable large animal model for human obesity. A fatness locus has been mapped to pig chromosome 4 and most probably a similar locus resides on human chromosome 1q. A more precise definition of the pig-human homology as regards this region is currently being investigated.
