WBR0988: Difference between revisions

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|MainCategory=Biochemistry
|MainCategory=Biochemistry
|SubCategory=General Principles
|SubCategory=General Principles
|MainCategory=Biochemistry
|MainCategory=Biochemistry
|MainCategory=Biochemistry
|MainCategory=Biochemistry
|MainCategory=Biochemistry
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|SubCategory=General Principles
|SubCategory=General Principles
|Prompt=A 25 year old male presents to the emergency department for acute chest pain radiating to the left arm and associated with nausea and sweating.  EKG reveals ST elevation in the anterior leads and the troponin level is elevated. The patient was admitted to the cath laboratory and appropriate management was initiated.  Further investigations reveal an elevated level of homocysteine and methionine in the blood and urine.  Supplementation with which of the following vitamins could possibly improve the condition of this patient?
|Prompt=A 25 year old male presents to the emergency department for acute chest pain radiating to the left arm and associated with nausea and sweating.  EKG reveals ST elevation in the anterior leads and the troponin level is elevated. The patient was admitted to the cath laboratory and appropriate management was initiated.  Further investigations reveal an elevated level of homocysteine and methionine in the blood and urine.  Supplementation with which of the following vitamins could possibly improve the condition of this patient?
|Explanation=Classic [[homocystinuria]] is an autosomal recessive disorder of the metabolism of the amino acid [[methionine]].  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, as seen in this patient, as well as with [[myopia]], [[ectopia lentis]] and [[marfanoid feature]]s.  Mild cases of classic homocystinuria are responsive to [[pyridoxine]] (vitamin B6) supplementation.
|Explanation=Classic [[homocystinuria]] is an autosomal recessive disorder of [[methionine]] metabolism.  The amino acid methione is usually 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, as seen in this patient, as well as with [[myopia]], [[ectopia lentis]] and [[marfanoid feature]]s.  Mild cases of classic homocystinuria are responsive to [[pyridoxine]] (vitamin B6) supplementation.
 
'''Educational objective:'''
Classical [[homocystinuria]] is an autosomal recessive disorder of the metabolism of the amino acid [[methionine]].  Mild cases of classic homocystinuria are responsive to [[pyridoxine]] (vitamin B6) supplementation.
 
'''Reference:'''


Reish, O., Townsend, D., Berry, S. A., Tsai, M. Y., King, R. A. 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. 57: 127-132, 1995.<br>
First aid for USMLE step 1, 2013.  Page 109.
|AnswerA=Pyridoxine
|AnswerA=Pyridoxine
|AnswerAExp=[[Pyridoxine]] (vitamin B6) might increase the activity of the enzyme [[cystathionine synthase]] in mild pyridoxine cases of [[homocystinuria]].
|AnswerAExp=[[Pyridoxine]] (vitamin B6) might increase the activity of the enzyme [[cystathionine synthase]] in mild pyridoxine cases of [[homocystinuria]].
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|AnswerE=Riboflavin
|AnswerE=Riboflavin
|AnswerEExp=[[Pyridoxine]] (vitamin B6), and not [[riboflavin]] (vitamin B2), might increase the activity of the enzyme [[cystathionine synthase]] in mild pyridoxine cases of [[homocystinuria]].
|AnswerEExp=[[Pyridoxine]] (vitamin B6), and not [[riboflavin]] (vitamin B2), might increase the activity of the enzyme [[cystathionine synthase]] in mild pyridoxine cases of [[homocystinuria]].
|EducationalObjectives=Classical [[homocystinuria]] is an autosomal recessive disorder of the metabolism of the amino acid [[methionine]].  Mild cases of classic homocystinuria are responsive to [[pyridoxine]] (vitamin B6) supplementation.
|References=Reish, O., Townsend, D., Berry, S. A., Tsai, M. Y., King, R. A. 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. 57: 127-132, 1995.<br>
First Aid 2015 page 108
|RightAnswer=A
|RightAnswer=A
|WBRKeyword=Homocystinuria, Pyridoxine,
|WBRKeyword=Homocystinuria, Pyridoxine, Metabolism, Biochemistry, Genetics, Vitamins, Nutrition, Amino acids.
|Approved=No
|Approved=Yes
}}
}}

Revision as of 18:36, 20 April 2015
Author [[PageAuthor::Rim Halaby, M.D. [1]]]
Exam Type ExamType::USMLE Step 1
Main Category MainCategory::Biochemistry
Sub Category SubCategory::General Principles
Prompt [[Prompt::A 25 year old male presents to the emergency department for acute chest pain radiating to the left arm and associated with nausea and sweating. EKG reveals ST elevation in the anterior leads and the troponin level is elevated. The patient was admitted to the cath laboratory and appropriate management was initiated. Further investigations reveal an elevated level of homocysteine and methionine in the blood and urine. Supplementation with which of the following vitamins could possibly improve the condition of this patient?]]
Answer A AnswerA::Pyridoxine
Answer A Explanation [[AnswerAExp::Pyridoxine (vitamin B6) might increase the activity of the enzyme cystathionine synthase in mild pyridoxine cases of homocystinuria.]]
Answer B AnswerB::Thiamine
Answer B Explanation [[AnswerBExp::Pyridoxine (vitamin B6), and not thiamine (vitamin B1), might increase the activity of the enzyme cystathionine synthase in mild pyridoxine cases of homocystinuria.]]
Answer C AnswerC::Biotin
Answer C Explanation [[AnswerCExp::Pyridoxine (vitamin B6), and not biotin (vitamin B7), might increase the activity of the enzyme cystathionine synthase in mild pyridoxine cases of homocystinuria.]]
Answer D AnswerD::Folic acid
Answer D Explanation [[AnswerDExp::Pyridoxine (vitamin B9), and not folic acid (vitamin B1), might increase the activity of the enzyme cystathionine synthase in mild pyridoxine cases of homocystinuria.]]
Answer E AnswerE::Riboflavin
Answer E Explanation [[AnswerEExp::Pyridoxine (vitamin B6), and not riboflavin (vitamin B2), might increase the activity of the enzyme cystathionine synthase in mild pyridoxine cases of homocystinuria.]]
Right Answer RightAnswer::A
Explanation [[Explanation::Classic homocystinuria is an autosomal recessive disorder of methionine metabolism. The amino acid methione is usually 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, as seen in this patient, as well as with myopia, ectopia lentis and marfanoid features. Mild cases of classic homocystinuria are responsive to pyridoxine (vitamin B6) supplementation.

Educational Objective: Classical homocystinuria is an autosomal recessive disorder of the metabolism of the amino acid methionine. Mild cases of classic homocystinuria are responsive to pyridoxine (vitamin B6) supplementation.
References: Reish, O., Townsend, D., Berry, S. A., Tsai, M. Y., King, R. A. 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. 57: 127-132, 1995.
First Aid 2015 page 108]]

Approved Approved::Yes
Keyword WBRKeyword::Homocystinuria, WBRKeyword::Pyridoxine, WBRKeyword::Metabolism, WBRKeyword::Biochemistry, WBRKeyword::Genetics, WBRKeyword::Vitamins, WBRKeyword::Nutrition, WBRKeyword::Amino acids.
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