Minerals: fluoride excess: 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.

Try it

Biochemistry · Minerals: fluoride excess

Sample item

A village with borewell water containing 4 mg/L fluoride has residents with brown mottled teeth, back stiffness and genu valgum in adolescents. What is the best explanation of the skeletal changes?

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

The answer and the reasoning

D. Fluoride enters hydroxyapatite as fluorapatite and stimulates osteoblasts, producing dense brittle bone and ligament calcification

Chronic excess fluoride replaces hydroxyl in hydroxyapatite, disrupts ameloblast function causing mottled enamel, and stimulates osteoblasts to produce dense, structurally abnormal bone with calcification of ligaments. The recommended upper limit in drinking water is about 1 to 1.5 mg/L. Deficiency instead raises caries risk.

Option by option

  • A. Vitamin D deficiency causes unmineralised osteoid

    Vitamin D deficiency causes soft, bowed bones with osteomalacia and not dense bone.

  • B. Defective collagen cross-linking causes brittle bone

    Defective collagen cross-linking is seen in lathyrism and copper deficiency, not fluorosis.

  • C. Excess parathyroid hormone causes subperiosteal resorption

    Hyperparathyroidism produces bone resorption and does not explain mottled teeth.

  • D. Fluoride enters hydroxyapatite as fluorapatite and stimulates osteoblasts, producing dense brittle bone and ligament calcification (correct)

    Correct. Fluorapatite and osteoblast stimulation underlie skeletal fluorosis.

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.

More Biochemistry questions

Questions about this Biochemistry question

What is the answer to this Biochemistry question?

The best answer is D, Fluoride enters hydroxyapatite as fluorapatite and stimulates osteoblasts, producing dense brittle bone and ligament calcification. Chronic excess fluoride replaces hydroxyl in hydroxyapatite, disrupts ameloblast function causing mottled enamel, and stimulates osteoblasts to produce dense, structurally abnormal bone with calcification of ligaments.

Why is "Vitamin D deficiency causes unmineralised osteoid" not the answer?

Vitamin D deficiency causes soft, bowed bones with osteomalacia and not dense bone.

Why is "Defective collagen cross-linking causes brittle bone" not the answer?

Defective collagen cross-linking is seen in lathyrism and copper deficiency, not fluorosis.

Why is "Excess parathyroid hormone causes subperiosteal resorption" not the answer?

Hyperparathyroidism produces bone resorption and does not explain mottled teeth.

What concept does this question test?

It tests Minerals: fluoride excess in Biochemistry. The recommended upper limit in drinking water is about 1 to 1.5 mg/L. Deficiency instead raises caries risk.

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 Minerals: fluoride excess?

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.