CCND1 and cleft palate: In summary, our findings and those of others suggest that excessive intake of retinoic acid during pregnancy leads to reduced cell proliferation through dysregulation of CCND1 and CDKN1B mediated by the miR-4680-3p–ERBB2–ERK1/2–CCND1/CDKN1B cascade in palatal mesenchymal cells, ultimately leading to cleft palate.