NBME 6 Ques (endocrine) - haqm

[ArchivalUser]

A 15-year-old girl is virilizing adrenal hyperplasia. Increased serum concentrations of 11-deoxycorticosterone have resulted in hypernatremia, hypokalemia, and hypervolemia. Serum ACTH concentration is increased, but serum aldosterone concentration is decreased. Administration of dexamethasone normalizes the ACTH, 11-deoxycorticosterone, aldosterone, and androgen concentrations. Which of the following labeled enzymes is most likely to be defective in this patient?

A) Cholesterol side-chain cleavage enzyme to yield pregnenolone
B) 17-alpha-hydroxylase (converts pregnenolone to 17-hydroxypregnenolone)
C) C 17-20 lyase (converts 17-hydroxypregnenolone to dehydroepiandrosterone)
D) 3-beta-hydroxysteroid dehydrogenase: delta 6,6 isomerase
E) 21-hydroxylase
F) 11-beta-hydroxylase
G) 18-hydroxylase
H) 18-hydroxydehydrogenase
I) 17-ketoreductase

[ArchivalUser]

G) 18 hydroxylase

[ArchivalUser]

EE

[ArchivalUser]

so far 2 diff ans any explanations..

[ArchivalUser]

change my answer to FF

[ArchivalUser]

11 B OH is missing so 11 -DOC rises weak mineralocorticoid will increase Na+ and 11 B OH deficiency will cause deficiency in cortisol which will cause negative feedback causing high ACTH,
since 17 OH is fine... the Androgen pathway will be more active leading to virilization.

[ArchivalUser]

Increase serum 11 deoxycorticosterone & decrease aldosterone indicates either 11 hydroxylase or 18 hydroxylase deficiency. now exclude between next two enzyme. As 11 deoxycorticosterone increased that means enzyme next to it absent which means 11 hydroxylase.

[ArchivalUser]

@jejuni, thanx a bunch. the 17 OH hyperactivity hadnt hit me. thanxs. the whole dexamethasone suppression test had me thrown off