USMLE PRACTICE QUESTION #59
TOPIC: Biochemistry/Pathology
Today’s question will test your understanding of a high-yield biochemistry disorder.
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A 6-month-old male is undergoing assessment by his pediatrician due to the recent onset of diminished mobility and episodes of uncontrolled shaking. He was delivered at 38 weeks’ gestation without any notable complications. There is no pertinent family history. Physical examination demonstrates global hypotonia and hyperreflexia in all four limbs. There are no signs of abdominal tenderness or organomegaly. On visual inspection, a red spot is noticeable on the macula. Which of the following is most likely to be observed in this patient?
A. Hyperacusis
B. Angiokeratomas
C. Corneal clouding
D. Lipid-laden macrophages
E. Gingival hyperplasia
Detailed Breakdown of Answers + Correct Answer Below ⏬
ANSWER + QUESTION BREAKDOWN
The mental model used to answer this question comes from our detailed test-taking skills masterclass. Here’s how to think through this question:
Step 1. Read the last line to determine what the question is asking: What additional finding is most likey to be found?
Step 2: Is this a first-, second-, or third-order question?
Answer: 2nd order: 1st. Diagnose with the disorder. 2nd. Be able to identify the finding consistent with your diagnosis.
Step 3. Read the vignette to gather information.
Step 4. Consider the question and ask yourself the most likely answer.
Step 5. Look at the answer choices and select the option most closely resembling your thoughts from “Step 4” above.
GENERAL ANALYSIS
Based on the clinical presentation and findings, the patient likely suffers from Tay-Sachs disease. In Tay-Sachs disease, there is an accumulation of GM2 gangliosides due to a deficiency in the enzyme Hexosaminidase A. This condition is associated with neurological symptoms and specific sensory issues.
ANSWER CHOICES:
ANSWER CHOICE A: Hyperacusis
Explanation: Hyperacusis refers to an increased sensitivity to normal environmental sounds. It may be associated with several conditions, including Tay-Sachs disease.
ANSWER CHOICE B: Angiokeratomas
Explanation: Angiokeratomas are skin lesions associated with Fabry disease. It is not associated with Tay-Sachs disease.
ANSWER CHOICE C: Corneal clouding
Explanation: Corneal clouding is commonly seen in mucopolysaccharidoses such as Hurler syndrome. It is not associated with Tay-Sachs disease.
ANSWER CHOICE D: Lipid-laden macrophages
Explanation: Lipid-laden macrophages, or foam cells, are typically found in Gaucher disease, not Tay-Sachs.
ANSWER CHOICE E: Gingival hyperplasia
Explanation: Gingival hyperplasia can occur as a side-effect of certain medications, including phenytoin.
FINAL VERDICT…
Hyperacusis is a characteristic feature of Tay-Sachs disease due to its neurological impact. The presence of a cherry-red spot on the macula, along with symptoms such as hypotonia and hyperreflexia, supports the diagnosis of a lysosomal storage disease like Tay-Sachs.
Two crucial and high-yield USMLE points to remember about Tay-Sachs disease include the deficient enzyme and the accumulated substance:
Deficient enzyme: Hexosaminidase A
Accumulated substance: GM2 gangliosides.
CORRECT ANSWER: A) Hyperacusis
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