Genetic and metabolic disorders: nephropathic cystinosis: practice question

A Pediatrics 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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Pediatrics · Genetic and metabolic disorders: nephropathic cystinosis

Sample item

A 14-month-old has poor growth, polyuria, polydipsia and florid rickets. Urine shows glycosuria with a normal blood glucose, generalised aminoaciduria and phosphaturia. Slit-lamp examination shows corneal crystals. Which drug specifically slows the renal decline?

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

The answer and the reasoning

D. Oral cysteamine

Nephropathic cystinosis is a lysosomal transport defect with renal Fanconi syndrome and corneal crystals. Cysteamine converts stored cystine into a form that leaves the lysosome and delays renal failure. Phosphate, bicarbonate and vitamin D replace the tubular losses.

Option by option

  • A. Oral nitisinone

    Nitisinone treats hereditary tyrosinaemia type 1 by blocking an upstream enzyme.

  • B. Sodium benzoate

    Sodium benzoate provides an alternative route for nitrogen excretion in urea cycle defects.

  • C. Oral penicillamine

    Penicillamine is a copper chelator for Wilson disease and a thiol drug for cystinuria, and it does not clear lysosomal storage.

  • D. Oral cysteamine (correct)

    Correct. Cysteamine depletes the stored amino acid inside lysosomes and delays renal failure.

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 Pediatrics question

What is the answer to this Pediatrics question?

The best answer is D, Oral cysteamine. Nephropathic cystinosis is a lysosomal transport defect with renal Fanconi syndrome and corneal crystals.

Why is "Oral nitisinone" not the answer?

Nitisinone treats hereditary tyrosinaemia type 1 by blocking an upstream enzyme.

Why is "Sodium benzoate" not the answer?

Sodium benzoate provides an alternative route for nitrogen excretion in urea cycle defects.

Why is "Oral penicillamine" not the answer?

Penicillamine is a copper chelator for Wilson disease and a thiol drug for cystinuria, and it does not clear lysosomal storage.

What concept does this question test?

It tests Genetic and metabolic disorders: nephropathic cystinosis in Pediatrics. Cysteamine converts stored cystine into a form that leaves the lysosome and delays renal failure. Phosphate, bicarbonate and vitamin D replace the tubular losses.

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 Genetic and metabolic disorders: nephropathic cystinosis?

Memorise milestones and the vaccine schedule as tables and revise them often. Then use the flashcards and the other Pediatrics 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.