Gene knockout by mutation is commonly carried out in bacteria. An early instance of the use of this technique in Escherichia coli was published in 1989 by Hamilton, et al. In this experiment, two sequential recombinations were used to delete the gene. This work established the feasibility of removing or replacing a functional gene in bacteria. That method has since been developed for other organisms, particularly research animals, like mice. Knockout mice are commonly used to study genes with human equivalents that may have significance for disease. An example of a study using knockout mice is an investigation of the roles of Xirp proteins in Sudden Unexplained Nocturnal Death Syndrome (SUNDS) and Brugada Syndrome in the Chinese Han Population.