Four of the five causative genes of CMCD are directly involved in IL17 signaling and encode the cytokine IL17F (IL17F), IL17 receptors (IL17RA and IL17RC) (201, 254), and ACT1 (TRAF3IP2), a membrane-proximal adaptor of IL17 receptor (255, 256) (Table 8). The gene discussed is IL17F; the disease is cutaneous mastocytosis.