This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Vitamins and Minerals, Subject name: Biochemistry
Isotretinoin is: 
Select and explain. 
A. All trans retinoic acid, B. All cis retinoic acid, C. 13 trans retinoic acid, D. 13 cis retinoic acid
D: 13 cis retinoic acid
Answer: D: 13 cis retinoic acid 
Explanation: Isotretinoin is a synthetic retinoid i.e. 13 cis retinoic acid uses:- Acne vulgaris Oral leukoplakia Pityriasis rubra pilaris Side effects:- Alopecia Tendon rupture/tendinitis Elevation of Lipoprotein (a) Teratogenicity. All-trans retinoic acid is involved in cell differentiation. All-trans retinoic acid binds to nuclear receptors (retinoic acid receptors). The activated retinoic acid-receptor complex interacts with response elements on the DNA and regulates the transcription of specific genes in different tissues. Ex: Control of expression of keratin gene in epithelial tissues. NOTE: All-trans retinoic acid (ATRA) is used in the treatment of acute promyelocytic leukemia.