Thursday, October 18, 2018
Repeated USMLE Questions Step 1- 235
A 4 year-old boy visits you in the clinic with his mother for evaluation of an increasing size of his genitalia. She tells you that her boy had aggressive behavior for the last six months. Besides progressive increase of the length of his penis, he has excessive pubic hair. On examination, his pulse is 80/min. and blood pressure is 140/92 mmHg. Other than genital findings, the rest of examination is normal. You send blood and urine samples for lab testing.
What is the most likely initial diagnosis of this boy’s condition?
A- Conn syndrome
B- C-21 hydroxylase deficiency
C- C-11 hydroxylase deficiency
D- C-17 hydroxylase deficiency
This patient has a typical presentation of C-11 hydroxylase deficiency. It is manifested as hypertension, precocious puberty and abnormal behavior. This enzyme contributes to the transformation of 11-deoxycorticosterone into corticosterone which in turn forms aldosterone and also assists in the transformation of 11-deoxycortisol into cortisol. So, deficiency of this enzyme leads to lack of cortisone and aldosterone. 11-deoxycorticosterone has the same action as aldosterone on the kidneys leading to Na and water retention which results in high blood pressure. Deficiency of cortisol leads to adrenal hyperplasia due to feedback stimulation of ACTH. Increased secretion of sex hormones leads to precocious puberty.
Conn syndrome is familial hyperaldosteronism characterized by hypertension, hypokalemia and metabolic alkalosis. Sex hormones are not affected in this disorder.
C 21-hydroxylase deficiency results also in low cortisol and aldosterone and high secretion of sex hormones. It leads to hypotension and precocious puberty due to accumulation of progesterone and its transformation into testosterone by zona reticularis.
C 17-hydroxylase enzyme stimulates the transformation of pregnenolone and progesterone into sex hormones secreted by zona reticularis. Deficiency of this enzyme leads to hypertension and delayed puberty.
The correct answer is C