Familial Crohn's disease in multiple siblings: no linkage to the HLA system.

We report five families with 3 or more children having Crohn's disease. In one family, 6 out of 11 siblings were affected. HLA haplotype study in affected children showed that the probability of random segregation was only 38 percent, making improbable a linkage between the histocompatibility locus and the development of Crohn's disease. However similar clinical patterns in siblings could suggest a genetic factor not linked to the HLA system.