Etiology and Pathogenesis



The cause of IBD is not known; therefore spec­ulations abound:
Genetic Factors. The marked difference in in­cidence in ethnic groups, the occasional occur­rence in monozygotic twins, and the tendency of IBD to cluster in families have suggested genetic or host factors, but no consistent genetic markers have been found.
Infectious Origin. Despite many reports, no agent has been consistently isolated.

Immunological Origin. The extraintestinal manifestations (see below), the reported presence of antibodies to colonic epithelial cells and of cy­totoxic T cells, and the clinical and histological responses to immunosuppressive agents have sug­gested an immunological basis for intestinal in­jury. Many of the immunological abnormalities described are quite likely to be secondary, how­ever.
Psychological Origin. Few believe that emo­tional factors are etiologic, but they may exacer­bate symptoms and impair the ability to cope with the chronicity and debility of IBD.

In brief there may indeed be important inher­ited factors determining host susceptibility, but environmental factors (infectious?, noninfectious antigens or toxins?) are probably immediately causative. With increasing technological devel­opment in Asia, for example, the incidence of IBD is increasing.