WBR0989

Author	[[PageAuthor::Yazan Daaboul, M.D. (Reviewed by Yazan Daaboul, M.D.)]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Biochemistry
Sub Category	SubCategory::General Principles
Prompt	[[Prompt::A 22-year-old man is brought by his roommate to the emergency department for acute motor weakness 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 arm. Brain CT scan reveals no bleeding. Brain MRI is remarkable for changes consistent with an acute ischemic stroke. Further laboratory evaluation is significant for elevated concentrations of homocysteine in the blood and urine. The patient is then diagnosed with a hereditary disease, and is transferred to ophthalmologic check-up. Which of the following is characteristic of the lens subluxation that is associated with this patient's condition?]]
Answer A	AnswerA::Downwards and outwards
Answer A Explanation	AnswerAExp::Homocystinuria is associated with lens subluxation that is downwards and inwards.
Answer B	AnswerB::Downwards and inwards
Answer B Explanation	AnswerBExp::Homocystinuria is associated with lens subluxation that is downwards and inwards.
Answer C	AnswerC::Upwards and outwards
Answer C Explanation	AnswerCExp::Homocystinuria is associated with lens subluxation that is downwards and inwards.
Answer D	AnswerD::Upwards and inwards
Answer D Explanation	AnswerDExp::Homocystinuria is associated with lens subluxation that is downwards and inwards.
Answer E	AnswerE::No specific association
Answer E Explanation	AnswerEExp::Homocystinuria is associated with lens subluxation that is downwards and inwards.
Right Answer	RightAnswer::B
Explanation	[[Explanation::Classic homocystinuria is an autosomal recessive hereditary 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 features. Ectopia lentis is commonly characterized by lens subluxation that is usually downwards and inwards. Educational Objective: Homocystinuria is associated with development of ophthalmic complications, such as early myopia and ectopia lentis. Ectopia lentis is commonly characterized by lens subluxation that is usually downwards and inwards. References: Makris M. Hyperhomocysteinemia and thrombosis. Clin Lab Haematol. 2000;22(3):133-143. First Aid 2015 page 108]]
Approved	Approved::Yes
Keyword	WBRKeyword::Stroke, WBRKeyword::Homocystinuria, WBRKeyword::Ectopia lentis, WBRKeyword::Autosomal recessive, WBRKeyword::Lens dislocation, WBRKeyword::Opthalmic complications, WBRKeyword::Eye, WBRKeyword::Genetics, WBRKeyword::Metabolism, WBRKeyword::Thrombosis, WBRKeyword::Homocysteine
Linked Question	Linked::
Order in Linked Questions	LinkedOrder::