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 suddenly he felt his left hand and arm heavy and numb. Brain CT scan reveals no bleeding; however, brain MRI reveals changes consistent with an acute ischemic stroke. Complete laboratory evaluation was ordered and it revealed elevated levels 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 outwards |
| 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. |
| Approved | Approved::No |
| Keyword | WBRKeyword::Homocystinuria, WBRKeyword::lens dislocation |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |