The function of ENSG00000139988 (RDH12, retinol dehydrogenase 12) is as follows. Retinoids dehydrogenase/reductase with a clear preference for NADP. Displays high activity towards 9-cis, 11-cis and all-trans- retinal. Shows very weak activity towards 13-cis-retinol (PubMed:12226107, PubMed:15865448). Also exhibits activity, albeit with lower affinity than for retinaldehydes, towards lipid peroxidation products (C9 aldehydes) such as 4-hydroxynonenal and trans-2-nonenal (PubMed:15865448, PubMed:19686838). May play an important function in photoreceptor cells to detoxify 4-hydroxynonenal and potentially other toxic aldehyde products resulting from lipid peroxidation (PubMed:19686838). Has no dehydrogenase activity towards steroids (PubMed:12226107, PubMed:15865448). {ECO:0000269|PubMed:12226107, ECO:0000269|PubMed:15865448, ECO:0000269|PubMed:19686838}.