The great interest in identifying susceptibility genes in inflammatory bowel diseases (IBD) has recently triggered the aggregation of family trees throughout Europe and the United States. This has led to a better knowledge of empirical risk and clinical characteristics of familial IBD. One of the most consistent findings in families with Crohn’s disease was early onset in most affected children of an affected parent, with an average difference of 15 years. This may be a more general feature of familial IBD, as shown in this issue by Lee et al (see page 808) who observed a similar time span (16–18 years) between generations in 50 pure Crohn’s disease, 51 pure ulcerative colitis and 36 mixed disease families.

Genetic anticipation has been suggested as a possible explanation for this finding.1 This term denotes a decrease in the age of onset and an increase in severity as a disease is passed through generations.2 Genetic anticipation has been described in monogenic neurological illnesses such as Huntington’s disease, myotonic dystrophy and more recently Friedreich’s ataxia. In these diseases, …