Misguided myeloid DC model of pathogenesis. According to this model, the stage of differentiation in which pathologic ERK activation arises determines the clinical manifestations of LCH, JXG, and ECD. Activating mutations in hematopoietic stem cells or undifferentiated myeloid DC precursors result in multifocal disseminated disease, whereas mutations in tissue-restricted precursors results in multifocal disease with lesions in limited tissues, and mutations in more differentiated tissue restricted precursor cells results in a single lesion.