Audio Qbank – HY USMLE Q #554 – Congenital adrenal hyperplasia

A 3-day-old girl is brought to the physician because of vomiting throughout the night following breastfeeding. Physical examination shows dry mucous membranes and lethargy. Serum studies show:

Sodium                                                                         138 mEq/L
Potassium                                                                   6.5 mEq/L
Bicarbonate                                                               18 mEq/L
Glucose                                                                         50 mg/dL
17-hydroxyprogesterone                                   Increased

Which of the following is the most likely deficient enzyme in this patient?

20,22-Desmolase
11β-hydroxylase
17α-hydroxylase
21-hydroxylase