“…Familial and twins evidence indicates that predisposition to ulcerative colitis is determined by genetic factors (Wigley and MacLaurin, 1962;Almy and Plaut, 1965;Morris, 1965;Binder, Weeke, Olsen, Anthonisen, and Riis, 1966;Davidson, 1967). If the sex ratio for the early-onset group of ulcerative colitis is to be explained in genetic terms, then it seems that an X-linked factor has a dominant expression in some populations, to give a female preponderance, and a recessive expression in others, where male patients predominate.…”