Genetics versus environment in inflammatory bowel disease: results of a British twin study

Abstract
The National Association for Colitis and Crohn's Disease is a patient support group with about 16000 members with inflammatory bowel disease. All members were asked to complete and return a prepaid postcard if they had inflammatory bowel disease and were born as one of a twin pair. Those replying were sent a follow up questionnaire to obtain details of the member's diagnosis and twin. Zygosity was determined with a validated questionnaire.3