Carbohydrate absorption: SGLT1 defect: 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 · Carbohydrate absorption: SGLT1 defect

Sample item

A newborn develops severe watery acidic diarrhoea and dehydration on every breast or lactose formula feed. The diarrhoea persists with a lactose-free glucose polymer formula but stops promptly when a fructose-based formula is given. Which transporter is defective?

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

The answer and the reasoning

C. Sodium-glucose cotransporter 1 (SGLT1) of the intestinal brush border

Glucose-galactose malabsorption is an autosomal recessive defect of SGLT1. Glucose and galactose, whether free or from lactose, remain in the lumen and cause osmotic diarrhoea. Fructose is absorbed by GLUT5, which is intact, so a fructose-based formula is tolerated.

Option by option

  • A. GLUT5

    A GLUT5 defect would worsen with fructose, which is the opposite of the observed response.

  • B. Lactase-phlorizin hydrolase

    Lactase deficiency would improve on a lactose-free formula containing glucose polymers.

  • C. Sodium-glucose cotransporter 1 (SGLT1) of the intestinal brush border (correct)

    Failure of sodium-coupled glucose and galactose uptake explains the osmotic diarrhoea, with fructose absorbed normally.

  • D. GLUT4

    GLUT4 is the insulin-responsive transporter of muscle and fat and is not involved in intestinal absorption.

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, Sodium-glucose cotransporter 1 (SGLT1) of the intestinal brush border. Glucose-galactose malabsorption is an autosomal recessive defect of SGLT1.

Why is "GLUT5" not the answer?

A GLUT5 defect would worsen with fructose, which is the opposite of the observed response.

Why is "Lactase-phlorizin hydrolase" not the answer?

Lactase deficiency would improve on a lactose-free formula containing glucose polymers.

Why is "GLUT4" not the answer?

GLUT4 is the insulin-responsive transporter of muscle and fat and is not involved in intestinal absorption.

What concept does this question test?

It tests Carbohydrate absorption: SGLT1 defect in Biochemistry. Glucose and galactose, whether free or from lactose, remain in the lumen and cause osmotic diarrhoea. Fructose is absorbed by GLUT5, which is intact, so a fructose-based formula is tolerated.

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 Carbohydrate absorption: SGLT1 defect?

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.