Which of the following statements with regards to alpha feto-protein (AFP) is INCORRECT?

Question

BlackTom AI · Accepted Answer

Alpha-fetoprotein (AFP) binds circulating estrogens in the fetus, thereby preventing maternal estrogens from crossing into the fetal brain and causing feminization/masculinization effects. It does not preferentially bind testosterone.

1) Key concepts
- AFP is a fetal plasma protein produced by the yolk sac and fetal liver and is present in fetal circulation.
- In many mammals (classically shown in rodents), AFP binds estradiol with high affinity; this protects female fetuses from maternal estrogens that could masculinize the developing brain.
- Male fetuses produce testosterone in the testes; testosterone (or its metabolites) can enter the fetal brain and, after local aromatization to estradiol, contribute to masculinization. AFP does not neutralize fetal/testicular testosterone.

2) Step-by-step reasoning
- Option (c): AFP is indeed present in fetal circulation (produced by fetal tissues) — this is true.
- Option (b): AFP preferentially binds estrogens and prevents them entering the brain — this correctly states AFP’s protective role against maternal estrogens.
- Option (a): Because AFP binds maternal estrogens, it prevents developing females from being masculinized by maternal estrogens — this is a correct consequence.
- Option (d): Claims AFP preferentially binds testosterone and prevents masculinization by testosterone. This contradicts established physiology: AFP does not preferentially bind androgens; testosterone from the male fetus can enter the brain and be aromatized to estradiol to masculinize male neural circuits.

3) Calculations
- None required.

4) Why the correct answer is correct
- The incorrect statement is (d). AFP’s known binding specificity is for estrogens, not testosterone; thus (d) is false.

5) Why other options are incorrect or correct
- a, b, c are correct statements about AFP. e (“A and B”) would claim both A and B are incorrect, which is false because A and B are correct.

Conclusion: The incorrect statement is d) It preferentially binds testosterone and prevents them from entering the brain to cause masculinization of the female brain. This matches the provided answer.

Which of the following statements with regards to alpha feto-protein (AFP) is INCORRECT? 单项选择题

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