Tooth development and dental anatomy: genes in tooth agenesis: practice question

A Dentistry 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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Dentistry · Tooth development and dental anatomy: genes in tooth agenesis

Sample item

Several members of a family have missing permanent teeth (oligodontia) with no other syndromic features. Mutations in which pair of genes are most often found in such non-syndromic familial tooth agenesis?

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

The answer and the reasoning

B. MSX1 and PAX9

MSX1 and PAX9 are transcription factors needed for progression of the tooth germ beyond the bud stage, and their mutations are the commonest known cause of isolated familial tooth agenesis. Enamel and dentine genes alter tissues rather than tooth number.

Option by option

  • A. AMELX and ENAM

    These genes encode enamel matrix proteins and cause enamel defects with a normal tooth number.

  • B. MSX1 and PAX9 (correct)

    Correct. These transcription factor genes are needed for tooth germ development and their loss causes agenesis.

  • C. DSPP and DMP1

    These genes encode dentine matrix proteins and cause dentine defects with a normal tooth number.

  • D. PTCH1 and SMO

    These are hedgehog pathway genes linked to keratocysts and basal cell carcinomas, not isolated agenesis.

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 Dentistry question

What is the answer to this Dentistry question?

The best answer is B, MSX1 and PAX9. MSX1 and PAX9 are transcription factors needed for progression of the tooth germ beyond the bud stage, and their mutations are the commonest known cause of isolated familial tooth agenesis.

Why is "AMELX and ENAM" not the answer?

These genes encode enamel matrix proteins and cause enamel defects with a normal tooth number.

Why is "DSPP and DMP1" not the answer?

These genes encode dentine matrix proteins and cause dentine defects with a normal tooth number.

Why is "PTCH1 and SMO" not the answer?

These are hedgehog pathway genes linked to keratocysts and basal cell carcinomas, not isolated agenesis.

What concept does this question test?

It tests Tooth development and dental anatomy: genes in tooth agenesis in Dentistry. Enamel and dentine genes alter tissues rather than tooth number.

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 Tooth development and dental anatomy: genes in tooth agenesis?

Learn the dental formula, eruption ages and tooth structure once, as tables. Then use the flashcards and the other Dentistry 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.