The observation that CARD15, RIPK2, and NF-κB have been linked to leprosy (193), tuberculosis (195, 197, 198), and IBD (150, 199) by GWAS and other genetic studies in humans and mice, has led to speculation of a common etiology between mycobacterial diseases and Crohn’s disease (197, 200, 201). This evidence concerns the gene NOD2 and Crohn disease.