## **Core Concept**
The question revolves around a case of a 10-day-old male pseudohermaphrodite with a 46 XY karyotype and hypertension. This presentation suggests an issue with sexual differentiation and possibly a defect in steroidogenesis, given the hypertension.

## **Why the Correct Answer is Right**
The correct answer, **17α-hydroxylase deficiency**, is a rare cause of congenital adrenal hyperplasia (CAH). This enzyme is crucial for the production of cortisol, androgens, and estrogens from pregnenolone and progesterone. A deficiency leads to an inability to produce these steroids, resulting in an overproduction of mineralocorticoids (like aldosterone) due to the shunting of precursors towards the mineralocorticoid pathway. This explains the hypertension. Additionally, the lack of androgen production during fetal development leads to undervirilization or feminization in genetically male (46 XY) individuals, presenting as pseudohermaphroditism.

## **Why Each Wrong Option is Incorrect**
- **Option A:** Deficiency in **3β-hydroxysteroid dehydrogenase** leads to an inability to synthesize all classes of steroids (glucocorticoids, mineralocorticoids, androgens, and estrogens) from pregnenolone. This typically results in decreased production of aldosterone and cortisol, leading to hypotension, not hypertension.
- **Option B:** **21-hydroxylase deficiency** is the most common cause of CAH, leading to decreased production of cortisol and aldosterone, with an overproduction of androgens. This results in virilization of females, not pseudohermaphroditism in males, and typically does not cause hypertension.
- **Option C:** **11β-hydroxylase deficiency** is another form of CAH that leads to an overproduction of androgens and 11-deoxycorticosterone (a potent mineralocorticoid), causing hypertension. However, it usually results in virilization of females rather than male pseudohermaphroditism.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that **17α-hydroxylase deficiency** is a unique cause of CAH that presents with **hypertension** and **sexual infantilism or pseudohermaphroditism** in genetic males, due to the specific block in steroidogenesis that favors mineralocorticoid production.

## **Correct Answer: D. 17α-hydroxylase deficiency**