Crohn's disease in four members of a family, two of whom are dizygotic twins.

Familial occurrence of Crohn's disease (CD) is well known, but the disease is rarely reported to occur in dizygotic twins. We present an additional case of dizygotic twins, both of whom developed CD, from a family in which two other members are affected. The 16-year-old son contracted the disease 2 years before his 50-year-old father, and 13 years before his twin sister. Another sister was affected 6 years after the onset of the disease in the propositus. HLA haplotyping of the three children matched the Mendelian ratio. The multiple occurrence of CD in blood relatives, especially in siblings, emphasizes the importance of genetic factors in the development of this disease. This family history, however, could point to psychic influences promoting the occurrence of CD on the basis of a polygenic disease susceptibility.