Table 2.

Information on smoking habits. Only twin pairs concordant for smoking habits were used in the smoking analysis. Four twin pairs were excluded because one twin was a smoker and the other was not. Only twin pairs including UC patients were used for comparisons between smokers and non-smokers [16 pairs] due to the lack of twin pairs including CD patients and concordant smokers.

	CD	UC
Twins both smokers	0	5
Twins both non-smokers	4	11
Twins discordant for smoking	2	2

UC, ulcerative colitis; CD, Crohn’s disease.

Numbers in bold indicate twin pairs used in smoker VS non-smoker comparison.