Question:medium
A 13-year-old girl visits the gynaecology OPD with a complaint of not attaining menarche. Her karyotype is 46,XX. On examination, clitoromegaly is seen. Which enzyme is most likely deficient in this condition?
A 13-year-old girl visits the gynaecology OPD with a complaint of not attaining menarche. Her karyotype is 46,XX. On examination, clitoromegaly is seen. Which enzyme is most likely deficient in this condition?
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Think of the commonest cause of CAH, the one that virilises and salt-wastes.
Updated On: Jun 23, 2026
- 21 alpha-hydroxylase
- 11 beta-hydroxylase
- 17 alpha-hydroxylase
- 3 beta-hydroxysteroid dehydrogenase
Show Solution
The Correct Option is A
Solution and Explanation
Pattern recognition: 46,XX + clitoromegaly + primary amenorrhea = a virilised genetic female, the classic picture of congenital adrenal hyperplasia.
Now sort the four enzymes by what they do to androgens and BP:
21-hydroxylase deficiency: virilisation + salt wasting, BP low or normal. The commonest CAH (over 90 percent). Fits the clitoromegaly here.
11 beta-hydroxylase deficiency: virilisation + hypertension. Possible but rare; the stem mentions no BP clue, and frequency favours 21-hydroxylase.
17 alpha-hydroxylase deficiency: under-virilisation + hypertension. Would give absent secondary sexual characters, NOT clitoromegaly, so it is the opposite of this case.
3 beta-HSD deficiency: only mild ambiguity, uncommon.
Highest yield and best fit: 21 alpha-hydroxylase. Pick option a.
Now sort the four enzymes by what they do to androgens and BP:
21-hydroxylase deficiency: virilisation + salt wasting, BP low or normal. The commonest CAH (over 90 percent). Fits the clitoromegaly here.
11 beta-hydroxylase deficiency: virilisation + hypertension. Possible but rare; the stem mentions no BP clue, and frequency favours 21-hydroxylase.
17 alpha-hydroxylase deficiency: under-virilisation + hypertension. Would give absent secondary sexual characters, NOT clitoromegaly, so it is the opposite of this case.
3 beta-HSD deficiency: only mild ambiguity, uncommon.
Highest yield and best fit: 21 alpha-hydroxylase. Pick option a.
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