Functional consequences of NOD2/CARD15 mutations in Crohn disease.

Crohn disease (CD) is a chronic, relapsing inflammatory disorder of the gastrointestinal tract. Its etiology remained obscure until recently, when, through an overwhelming body of research, the main theme of its origin became clear. CD develops in individuals who carry risk alleles for the disease that can cause a loss of physiological tolerance to commensal bacteria. As a consequence, immune responses develop that activate a whole range of immunocompetent cells, resulting in the secretion of proinflammatory mediators that ultimately cause mucosal breaks and the formation of ulceration, edema, and loss of proper function.