Lysosomal storage disorders: practice question

A Biochemistry question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Biochemistry · Lysosomal storage disorders

Sample item

An 8-month-old infant has regression of milestones, exaggerated startle to sound, hypotonia and a cherry-red macular spot, with no hepatosplenomegaly or coarse facial features. Which enzyme is deficient?

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

D. Hexosaminidase A

Tay-Sachs disease is caused by deficiency of hexosaminidase A, which causes GM2 ganglioside to accumulate in neurons. It presents with neurodegeneration, a cherry-red spot and exaggerated startle, and organs are not enlarged.

Option by option

  • A. Arylsulfatase A

    Arylsulfatase A deficiency causes metachromatic leukodystrophy, a demyelinating disease.

  • B. Beta-galactosidase

    Beta-galactosidase deficiency causes GM1 gangliosidosis, which usually has coarse features and organomegaly.

  • C. Alpha-galactosidase A

    Alpha-galactosidase A deficiency causes Fabry disease, with limb pain and renal and cardiac involvement.

  • D. Hexosaminidase A (correct)

    Correct. Hexosaminidase A deficiency causes Tay-Sachs disease.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

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Questions about this Biochemistry question

What is the answer to this Biochemistry question?

The best answer is D, Hexosaminidase A. Tay-Sachs disease is caused by deficiency of hexosaminidase A, which causes GM2 ganglioside to accumulate in neurons.

Why is "Arylsulfatase A" not the answer?

Arylsulfatase A deficiency causes metachromatic leukodystrophy, a demyelinating disease.

Why is "Beta-galactosidase" not the answer?

Beta-galactosidase deficiency causes GM1 gangliosidosis, which usually has coarse features and organomegaly.

Why is "Alpha-galactosidase A" not the answer?

Alpha-galactosidase A deficiency causes Fabry disease, with limb pain and renal and cardiac involvement.

What concept does this question test?

It tests Lysosomal storage disorders in Biochemistry. It presents with neurodegeneration, a cherry-red spot and exaggerated startle, and organs are not enlarged.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Lysosomal storage disorders?

Build one table of enzyme deficiency, disease, inheritance and key finding, then revise it by spaced recall. Then use the flashcards and the other Biochemistry questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.