Editor,—A recent study of intestinal permeability in patients with Crohn’s disease, their spouses, and first degree relatives, has concluded that baseline permeability is influenced by environmental factors, whereas permeability provoked by acetylsalicylic acid is genetically determined (Gut1999;44:96–100). The significance of increased intestinal permeability is still unclear, but animal models show that it may be an early event in the inflammatory process, suggesting that environmental and hereditary factors interact in the pathogenesis of Crohn’s disease.

This study also observed that baseline permeability in relatives who were not living with the patient with Crohn’s disease at the time of diagnosis, or at the time of the permeability test, was considerably less abnormal than that of relatives who lived with the patient. Similarly, a subcategory of spouses who had lived with their Crohn’s disease partners since before diagnosis, had a higher percentage of increased permeability than other spouses.

Previously, increased occurrence of Crohn’s disease in a patient’s relatives has been assumed to be indicative of genetic predisposition, and has not been linked to frequency of contact. A study of clusters of cases from the same family suggested that, based on a temporal succession of presentations, an infectious microorganism might be …