View source for WBR0989

{{WBRQuestion
|QuestionAuthor={{Rim}}
|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 22 year old male is brought by his roommate to the emergency department for acute motor and sensation loss in his left arm.  The patient reports that he was studying with his roommate when he suddenly felt heaviness and numbness in his left hand and arm.  Brain CT scan reveals no bleeding.  Brain MRI reveals changes consistent with an acute ischemic stroke.  Complete laboratory evaluation is ordered and it is significant for an elevated level of [[homocysteine]] in the blood and urine.  Which of the following is characteristic of the lens subluxation that may be a complication of the patient's disease?
|Explanation=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.  [[Ectopia lentis]] is commonly characterized by lens subluxation downwards and inwards.
|AnswerA=Downwards and outwards
|AnswerAExp=Homocystinuria is associated with lens subluxation downwards and inwards.
|AnswerB=Downwards and inwards
|AnswerBExp=Homocystinuria is associated with lens subluxation downwards and inwards.
|AnswerC=Upwards and outwards
|AnswerCExp=Homocystinuria is associated with lens subluxation downwards and inwards.
|AnswerD=Upwards and inwards
|AnswerDExp=Homocystinuria is associated with lens subluxation downwards and inwards.
|AnswerE=No specific direction
|AnswerEExp=Homocystinuria is associated with lens subluxation downwards and inwards.
|EducationalObjectives=Classical [[homocystinuria]] is an autosomal recessive disorder in which metabolism of the amino acid methionine is impaired.  Homocystinuria is associated with atheroembolic events and lens subluxation downwards and inwards.
|References=Makris, M1. "Hyperhomocysteinemia and thrombosis." Clinical & Laboratory Haematology 22.3 (2000): 133-143.<br>
First Aid 2015 page 108
|RightAnswer=B
|WBRKeyword=Biochemistry, Stroke, Homocystinuria, Lens dislocation, Eye, Genetics, Metabolism, Thrombosis, Homocysteine,
|Approved=No
}}