Carbohydrate metabolism: familial renal glycosuria: 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 metabolism: familial renal glycosuria

Sample item

A healthy 25-year-old has persistent glucose in the urine on routine testing. Fasting and post-prandial plasma glucose, HbA1c and an oral glucose tolerance test are all normal. Which defect is most likely?

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

The answer and the reasoning

A. Mutation of the sodium-glucose cotransporter 2 in the proximal tubule

Familial renal glycosuria is usually an autosomal condition caused by mutations in SLC5A2, which encodes SGLT2, the transporter that reclaims most filtered glucose in the early proximal tubule. Plasma glucose is normal, so no treatment is needed. The same transporter is the target of the gliflozin drugs.

Option by option

  • A. Mutation of the sodium-glucose cotransporter 2 in the proximal tubule (correct)

    Correct. Loss of SGLT2 function lets filtered glucose escape reabsorption despite normal plasma levels.

  • B. Deficiency of galactokinase in the lens and liver

    Galactokinase deficiency causes galactose-related cataracts and galactosuria, not glucosuria.

  • C. Deficiency of the insulin-sensitive glucose transporter in muscle

    A defect of the insulin-sensitive transporter in muscle would give insulin resistance and raised plasma glucose.

  • D. Inactivating mutation of glucokinase in pancreatic beta cells

    Glucokinase inactivation causes mild raised fasting glucose (MODY2), which is not seen here.

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 A, Mutation of the sodium-glucose cotransporter 2 in the proximal tubule. Familial renal glycosuria is usually an autosomal condition caused by mutations in SLC5A2, which encodes SGLT2, the transporter that reclaims most filtered glucose in the early proximal tubule.

Why is "Deficiency of galactokinase in the lens and liver" not the answer?

Galactokinase deficiency causes galactose-related cataracts and galactosuria, not glucosuria.

Why is "Deficiency of the insulin-sensitive glucose transporter in muscle" not the answer?

A defect of the insulin-sensitive transporter in muscle would give insulin resistance and raised plasma glucose.

Why is "Inactivating mutation of glucokinase in pancreatic beta cells" not the answer?

Glucokinase inactivation causes mild raised fasting glucose (MODY2), which is not seen here.

What concept does this question test?

It tests Carbohydrate metabolism: familial renal glycosuria in Biochemistry. Plasma glucose is normal, so no treatment is needed. The same transporter is the target of the gliflozin drugs.

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 metabolism: familial renal glycosuria?

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.