Endocrinology: resistance to thyroid hormone: practice question

A Physiology 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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Physiology · Endocrinology: resistance to thyroid hormone

Sample item

A 9-year-old has a small goitre, tachycardia and hyperactivity. Free T4 and free T3 are raised, but TSH is within the normal range, and pituitary MRI is normal. His father has the same biochemical pattern. What is the most likely defect?

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

The answer and the reasoning

C. Thyroid hormone receptor beta mutation

Resistance to thyroid hormone is usually due to a dominant mutation in the thyroid hormone receptor beta gene. Feedback is set at a higher level, so TSH is not suppressed despite high free hormones, and the pattern runs in families.

Option by option

  • A. Stimulating antibodies against the TSH receptor

    Stimulating antibodies would suppress TSH and are not familial in this way.

  • B. An activating mutation of the TSH receptor

    An activating TSH receptor mutation would suppress TSH.

  • C. Thyroid hormone receptor beta mutation (correct)

    Correct. Reduced receptor responsiveness blunts feedback, so TSH stays unsuppressed in the face of high free hormones.

  • D. Raised thyroxine-binding globulin

    Raised binding globulin raises total hormone but leaves free hormone and TSH normal.

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 Physiology question

What is the answer to this Physiology question?

The best answer is C, Thyroid hormone receptor beta mutation. Resistance to thyroid hormone is usually due to a dominant mutation in the thyroid hormone receptor beta gene.

Why is "Stimulating antibodies against the TSH receptor" not the answer?

Stimulating antibodies would suppress TSH and are not familial in this way.

Why is "An activating mutation of the TSH receptor" not the answer?

An activating TSH receptor mutation would suppress TSH.

Why is "Raised thyroxine-binding globulin" not the answer?

Raised binding globulin raises total hormone but leaves free hormone and TSH normal.

What concept does this question test?

It tests Endocrinology: resistance to thyroid hormone in Physiology. Feedback is set at a higher level, so TSH is not suppressed despite high free hormones, and the pattern runs in families.

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 Endocrinology: resistance to thyroid hormone?

For each system, sketch the key graph (pressure–volume loop, oxygen dissociation curve, nephron handling) and explain it aloud. Then use the flashcards and the other Physiology 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.