One of the widely studied genes of retinol dehydrogenase RDH12, which encodes retinol dehydrogenase is part of the superfamily of short-chained alcohol dehydrogenases and reductases.
However, not all retinol dehydrogenases in visual cycle are identified, and this remains challenging to scientists due to the overlapping expressions and activity redundancy among two large RDH and RDH-like producing classes: microsomal short-chain dehydrogenase/reductase and cytosolic medium-chain alcohol dehydrogenases [REF].