**2.7 ALDHs (aldehyde dehydrogenases)**

ALDHs are cytoplasmic enzymes that convert/oxidize retinaldehyde to RA. ALDHs are the enzymes that function after the alcohol dehydrogenase step in the RA signaling pathway. Nineteen ALDH isoforms encoded by 19 different genes exist in humans with as many orthologs in the mouse plus some alternatively spliced transcriptional variants. Through its role in retinol metabolism, ALDHs play a major role in the regulation of responses to RA.
