View source for WBR0988

{{WBRQuestion
|QuestionAuthor={{YD}} (Reviewed by {{YD}})
|ExamType=USMLE Step 1
|MainCategory=Biochemistry
|SubCategory=General Principles
|MainCategory=Biochemistry
|SubCategory=General Principles
|MainCategory=Biochemistry
|SubCategory=General Principles
|MainCategory=Biochemistry
|MainCategory=Biochemistry
|MainCategory=Biochemistry
|SubCategory=General Principles
|MainCategory=Biochemistry
|SubCategory=General Principles
|MainCategory=Biochemistry
|SubCategory=General Principles
|MainCategory=Biochemistry
|SubCategory=General Principles
|MainCategory=Biochemistry
|MainCategory=Biochemistry
|SubCategory=General Principles
|Prompt=A 25-year-old man presents to the emergency department (ED) with acute chest pain radiating to the left arm. He states that his pain is associated with nausea and cold sweating.  In the ED, ECG is remarkable for ST-segment elevation in the anterior leads, and the serum troponin concentration is elevated. The patient is transferred to the catheterization laboratory for urgent percutaneous coronary intervention (PCI). The next day, further investigations are remarkable for elevated concentrations of homocysteine and methionine in the blood and urine. Supplementation with which of the following vitamins could possibly improve this patient's condition?
|Explanation=Classic [[homocystinuria]] is an autosomal recessive disorder characterized by impaired [[methionine]] metabolism.  The amino acid methione is normally converted to homocysteine during its degradation. In homocystinuria, this process is impaired. Homocystinuria is characterized by an accumulation of [[homocysteine]] in the serum and an increased excretion of homocysteine in the urine.  It is associated with thromboembolic events at an early age, early [[myopia]], [[ectopia lentis]], and [[marfanoid feature]]s. Mild cases of classic homocystinuria are responsive to [[pyridoxine]] (vitamin B6) supplementation.
|AnswerA=Pyridoxine
|AnswerAExp=[[Pyridoxine]] (vitamin B6) may increase the activity of the enzyme [[cystathionine synthase]] in mild cases of [[homocystinuria]].
|AnswerB=Thiamine
|AnswerBExp=[[Thiamine]] (vitamin B1) supplementation is indicated in [[Wernicke-Korsakoff syndrome]] and [[beriberi]].
|AnswerC=Biotin
|AnswerCExp=[[Biotin]] (vitamin B7) supplementation is indicated in biotin deficiency.
|AnswerD=Folate
|AnswerDExp=[[Folate]] (vitamin B9) supplementation is indicated among pregnant women and patients with megaloblastic anemia due to folate deficiency.
|AnswerE=Riboflavin
|AnswerEExp=[[Riboflavin]] (vitamin B2) supplementation is indicated in cheilosis (vitamin B2 deficiency).
|EducationalObjectives=Classical [[homocystinuria]] is an autosomal recessive disorder characterized by impaired methionine metabolism. Mild cases of classic homocystinuria are responsive to [[pyridoxine]] (vitamin B6) supplementation.
|References=Reish O, Townsend D, Berry SA, et al. Tyrosinase inhibition due to interaction of homocyst(e)ine with copper: the mechanism for reversible hypopigmentation in homocystinuria due to cystathionine beta-synthase deficiency. Am J Hum Genet. 1995;57:127-132.<br>
First Aid 2015 page 108.
|RightAnswer=A
|WBRKeyword=Homocystinuria, Pyridoxine, Metabolism, Biochemistry, Genetics, Vitamins, Nutrition, Amino acids, Myocardial infarction, STEMI
|Approved=Yes
}}