The nucleotide-binding oligomerization domain-containing protein 2 (Nod2) has been identified as a key factor for T1D susceptibility; Nod2−/−NOD mice had different gut microbiota compared to Nod2+/+NOD mice and were protected from diabetes, but only when kept separate from Nod2+/+NOD mice, suggesting that T1D susceptibility in Nod2−/−NOD mice is dependent on the alteration of gut microbiota. Here, NOD2 is linked to type 1 diabetes mellitus.