 Recent research suggests the microbiota the ecosystem of bacteria within the gut may trigger disease in susceptible individuals. Another important research area is the epigenome changes to the structure and regulation of our genome which occur throughout our life. It is known that siblings of Crohns Disease sufferers have a changes to the immune system characteristic of Crohn;s. However it is not known whether these changes are due to genetic similarity or shared environment. Comparison between mono and dizygotic twins elucidates the relative importance of genetic and environmental factors. 