Biomolecules and enzymes: lysosomal beta-galactosidase: 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 · Biomolecules and enzymes: lysosomal beta-galactosidase

Sample item

A 6-month-old infant has coarse facies, hepatosplenomegaly, skeletal dysplasia, hypotonia and a cherry-red macular spot. Storage of GM1 ganglioside and keratan sulfate fragments is found. Which enzyme is deficient?

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

The answer and the reasoning

C. Beta-galactosidase

GM1 gangliosidosis results from deficiency of lysosomal beta-galactosidase. This enzyme removes terminal galactose from GM1 ganglioside and from keratan sulfate, so neurological features are combined with dysostosis multiplex and visceromegaly.

Option by option

  • A. Alpha-galactosidase A

    Alpha-galactosidase A deficiency causes Fabry disease, with ceramide trihexoside accumulation in vessels and kidney.

  • B. Beta-hexosaminidase A

    Beta-hexosaminidase A deficiency causes Tay-Sachs disease with GM2 storage, without visceromegaly or skeletal dysplasia.

  • C. Beta-galactosidase (correct)

    Correct. Beta-galactosidase deficiency causes GM1 ganglioside and keratan sulfate storage.

  • D. Glucocerebrosidase

    Glucocerebrosidase deficiency causes Gaucher disease with glucocerebroside storage in macrophages.

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 C, Beta-galactosidase. GM1 gangliosidosis results from deficiency of lysosomal beta-galactosidase.

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

Alpha-galactosidase A deficiency causes Fabry disease, with ceramide trihexoside accumulation in vessels and kidney.

Why is "Beta-hexosaminidase A" not the answer?

Beta-hexosaminidase A deficiency causes Tay-Sachs disease with GM2 storage, without visceromegaly or skeletal dysplasia.

Why is "Glucocerebrosidase" not the answer?

Glucocerebrosidase deficiency causes Gaucher disease with glucocerebroside storage in macrophages.

What concept does this question test?

It tests Biomolecules and enzymes: lysosomal beta-galactosidase in Biochemistry. This enzyme removes terminal galactose from GM1 ganglioside and from keratan sulfate, so neurological features are combined with dysostosis multiplex and visceromegaly.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. 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 Biomolecules and enzymes: lysosomal beta-galactosidase?

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.