[The present and the prospect of study on Blau syndrome/early-onset sarcoidosis]

Blau syndrome (BS) and early-onset sarcoidosis (EOS) are both systemic granulomatous disease evoked by the mutated NOD2. It occurs in children younger than 4 years of age and is characterized by a distinct triad of skin, joint, and eye disorders without apparent pulmonary involvement. NOD2 encodes an intracellular receptor for muramyl dipeptide (MDP), the common component of bacterial cell wall peptidoglycan, and is expressed in cytoplasm of monocytic cells and epithelial cells. While its loss-of-function mutations are recognized in Crohn's disease, the mutations observed in BS/EOS are gain-of-function, and induced MDP-independent basal NF-kappaB activation. But we still do not know the precious molecular mechanism how the activation of NOD2 induces granuloma formation in the skin, joints and eyes.