Mutation, selection, and evolution of the Crohn disease susceptibility gene CARD15.

Three common mutations in the CARD15 (NOD2) gene are known to be associated with susceptibility to Crohn disease (CD), and genetic data suggest a gene dosage model with an increased risk of 2-4-fold in heterozygotes and 20-40-fold in homozygotes. However, the discovery of numerous rare variants of CARD15 indicates that some heterozygotes for the common mutations have a rare mutation on the other CARD15 allele, which would support a recessive model for CD. We addressed this issue by screening CARD15 for mutations in 100 CD patients who were heterozygous for one of the three common mutations.