A female child is brought with ambiguous genitalia and hyperpigmentation of skin. she has increased BP and hypokalemia. which of the following enzymes is deficient in this child?
**Core Concept**
The question describes a child with ambiguous genitalia, hyperpigmentation, hypertension, and hypokalemia, which are characteristic features of Congenital Adrenal Hyperplasia (CAH). CAH is a group of inherited disorders caused by the deficiency of enzymes involved in the biosynthesis of cortisol from cholesterol in the adrenal glands.
**Why the Correct Answer is Right**
The child's symptoms are due to an excess of androgens produced by the adrenal glands as a result of the enzyme deficiency. The excess androgens lead to virilization (ambiguous genitalia) and hyperpigmentation. The deficiency of the enzyme 21-hydroxylase is the most common cause of CAH, leading to an accumulation of 17-hydroxyprogesterone, which is then shunted towards the production of androgens. This also results in an overproduction of aldosterone, leading to hypertension and hypokalemia.
**Why Each Wrong Option is Incorrect**
* **Option A:** 17-alpha-hydroxylase deficiency is another cause of CAH, but it presents with hypertension and hypokalemia due to the overproduction of mineralocorticoids, but it doesn't typically cause ambiguous genitalia.
* **Option B:** 11-beta-hydroxylase deficiency is another form of CAH, but it typically presents with hypertension and hypokalemia due to the overproduction of 11-deoxycortisol, which has mineralocorticoid activity.
* **Option C:** 3-beta-hydroxysteroid dehydrogenase deficiency is a rare cause of CAH, and it presents with a more severe form of the disease, including salt-wasting and hypokalemia.
**Clinical Pearl / High-Yield Fact**
CAH due to 21-hydroxylase deficiency is the most common cause of ambiguous genitalia in newborns, and it is essential to diagnose and treat it promptly to prevent long-term consequences, such as infertility and cardiovascular disease.
**Correct Answer: D. 21-hydroxylase.**