HOXB6 and microtia: The RA signaling pathway has been reported to be related to microtia and regulates HOXB6. 1Using immunohistochemistry staining, we observed a decrease in the expression of RA receptor alpha (RARA) in the auricle cartilage of patients with microtia (Fig. 1M; Fig. S5A), and RARA serves as a marker of the RA signaling pathway.