Background: Two French families were investigated. In the first a husband, wife, and 4 children had Crohn's disease; in the second 7 of 11 children had the disease. There was no history of Crohn's disease in antecedent generations and no linkage to HLA haplotypes. Methods: Methods included family interviews; review of medical records, radiographs, and pathology slides; serology; selective stool culture; enzyme-linked immunosorbent assay for fecal viral detection; and immunocytochemlstry. Results: In both families multiple cases occurred among siblings in 7-13-month periods. There appeared to be a 4-&year recurrence of new disease in both families. Radiographs showed a remarkable similarity in the pattern of disease, confined to distal ileum and cecum, in the members of family 1. Examination for pathology showed granulomas in all 8 patients for whom tissues were available. Acid-fast organisms or Carnpylobacter-like organisms were not found in tissue sections, and immunocytochemistry was negative for mycobacteria and Yersinia. Stool cultures were negative for mycobacteria, Yersinia, and Mycoplasma. Torovirus and coronavirus antigens were not found in stool. Serology was negative for antibodies to Bruce/la, Yersinia, influenza, and three enteropathogenic viruses of animals. Conclusions: The circumstances and data suggest that an infectious microorganism is responsible for these clusterings of Crohn's disease. linkage study of the above kindred, one other French family, and three Belgian families with a high incidence of Crohn's disease.' The first study concluded that the occurrence of three cases within 10 months in members of a family living in the same house was evidence for an environmental etiology; the second study found an absence of HLA linkage in fa-milial Crohn's disease. In view of the rarity of such high frequencies of Crohn's disease among family members, we initiated an in-depth study of the two French families.
Family 1 consisted of a 52-year-old mother and 4 children, aged 20-30, all of whom had Crohn's disease. The father died of complications of Crohn's disease in 1986.
Family 2 consisted of a 59-year-old mother and 11 children, 
Enzyme-linked immunosorbent assay (ELISA) methods for antigen capture were used for the viruses."-i3 Sera from the same 10 patients and 5 unaffected family members were aliquoted and distributed for antibody determinations. An immunoblot method determined specific immunoglobulin A (IgA) and IgG antibodies to plasmid encoded virulence proteins (Yops 2a, 2b, 4a, and 5 and the V-antigen) of Y. enterocolitica and Yersinia pseudotuberculosis;' tube agglutination was used for Brucella abortus, which also recognizes Brucella suis and Brucela melitensis,'5 and mercap- 
Details regarding the onset and character of Crohn's disease, as well as pertinent historical data for family 1, are summarized in Table 1 
Radiographic features of the six patients from family 1 and seven from family 2 are illustrated in five had fistulas. One of the five subsequently developed a 17-cm segment of disease in the left colon, and the mother had ileal involvement exclusively.
In family 2, for one reason or another, retraction of 
By all accounts, history, physical findings, radiography, and pathology, the 6 patients in family 1 and the 7 in family 2 had Crohn's disease. The special stains, immunocytochemistry, microbiology, and serol- an infectious etiology. In family 1, two cases occurred in a 7-month period (1974) and two others in a 13month period (1982) (1983) ; in family 2, 4 of 11 children developed Crohn's disease in a lo-month period (1972) (1973) and 2 others in a subsequent IO-month time frame (1983) (1984) .
In two of these four aggregates, the children affected were bed partners before and at the time they developed Crohn's disease; in one other aggregate, the children shared a room. In each of these four aggregates, the children were not twins and they were not of the same age. In family 1, nonsanguinous husband and wife contracted Crohn's disease. The uniformity of ileal and cecal disease in family 1 is akin to that which might be expected had a uniform dose of an enteric pathogen been given to a genetically uniform group of experimental subjects, e.g., a litter of mice or piglets. There is the suggestion in this family that some microbial agent specifically targeted the terminal ileum and cecum, segments we know to be abundant in lymphoid follicles and M cells. in previous studies) that had been frozen and was terminated after 6 months, we failed to find acid-fast organisms or immunostained mycobacteria in the lesions. We also tested for evidence of other pathogens that produce enterocolitis or regional enteritis in ani- netic studies have not been neglected. Pedigree reviews will be completed and DNA analyses will follow.
1.
3.
6.