WBR0989

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 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?]]
Answer A	AnswerA::Downwards and outwards
Answer A Explanation	AnswerAExp::Homocystinuria is associated with lens subluxation downwards and inwards.
Answer B	AnswerB::Downwards and inwards
Answer B Explanation	AnswerBExp::Homocystinuria is associated with lens subluxation downwards and inwards.
Answer C	AnswerC::Upwards and outwards
Answer C Explanation	AnswerCExp::Homocystinuria is associated with lens subluxation downwards and inwards.
Answer D	AnswerD::Upwards and inwards
Answer D Explanation	AnswerDExp::Homocystinuria is associated with lens subluxation downwards and inwards.
Answer E	AnswerE::No specific direction
Answer E Explanation	AnswerEExp::Homocystinuria is associated with lens subluxation downwards and inwards.
Right Answer	RightAnswer::B
Explanation	[[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 features. Ectopia lentis is commonly characterized by lens subluxation downwards and inwards. Educational objective: Classical homocystinuria is an autosomal recessive disorder of the metabolism of the amino acid methionine. Homocystinuria is associated with lens subluxation downwards and inwards. Reference: First aid for USMLE step 1, 2013. Page 109. Educational Objective: References: ]]
Approved	Approved::No
Keyword	WBRKeyword::Homocystinuria, WBRKeyword::lens dislocation
Linked Question	Linked::
Order in Linked Questions	LinkedOrder::