Figure 3 The molecular mechanism for Barrett's metaplasia may result from change in the activation status of a gene as a result of injury. The example shown here is activation of gene “x” in the oesophagus. This hypothetical gene would ordinarily be switched off during embryogenesis when the oesophagus changes from a columnar‐lined epithelium to a squamous epithelium. Reactivation of that gene may lead to a patch of columnar tissue, which may then grow to occupy the lower part of the oesophagus as a result of clonal expansion. This process could also involve inactivation of a gene and there may be multiple genes involved.