The discovery of retinoid receptors has contributed greatly to our understanding of the mechanism of action of vitamin A. The organism produces at least two ligands from ingested vitamin A which act as hormones modulating the activity of numerous genes via their nuclear receptor. These ligands are produced locally by target cells from retinol and retinaldehyde. These advances do not respond to the clinicians' interrogation as to why 13cis retinoic acid blocks sebaceous secretion and cures severe acne while other known retinoids are uneffective. Current research would suggest that the expression of nuclear receptors is not altered in skin diseases but that upstream anomalies in the intracrine system (enzymes and binding proteins) could be involved. Clinically, teratogenic risks are a major obstacle to the oral administration of retinoids and the future in skin diseases lies most likely in topical applications.
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