Monozygotic twins with ulcerative colitis.

Monozygous twin sisters developed ulcerative colitis within 7 years of each other. Both had distal colitis confirmed by histology and radiology. Their maternal grandmother subsequently developed the disease. The long interval between the onset of the disease in the twins suggests a role for environmental factors in addition to genetic influences. Although about five hundred sets of twins with ulcerative colitis may be expected in Britain, this is the first set to be reported.