## **Core Concept**
The question revolves around a case of a 10-day-old male pseudohermaphrodite with a 46 XY karyotype and hypertension. The condition described points towards a disorder of sex development (DSD) with an underlying enzymatic deficiency affecting steroidogenesis, particularly in the context of Congenital Adrenal Hyperplasia (CAH) or a related condition.

## **Why the Correct Answer is Right**
The correct answer, **17α-hydroxylase deficiency**, is a rare cause of Congenital Adrenal Hyperplasia. This enzyme is crucial for the production of cortisol and sex steroids from pregnenolone. A deficiency leads to an inability to produce cortisol and sex hormones (like testosterone), but there is an overproduction of mineralocorticoids (like aldosterone) due to the shunting of precursors towards the mineralocorticoid pathway. The overproduction of mineralocorticoids results in hypertension and hypokalemia. The lack of fetal testicular androgen production results in undervirilization or feminization of a genetically male (46,XY) fetus, leading to male pseudohermaphroditism.

## **Why Each Wrong Option is Incorrect**
- **Option A: 21α-hydroxylase deficiency** is the most common cause of CAH, leading to a deficiency in cortisol and aldosterone production and an overproduction of androgens. This results in virilization of females and does not typically cause hypertension.
- **Option B: 11β-hydroxylase deficiency** is another form of CAH that leads to an overproduction of deoxycorticosterone (DOC), a potent mineralocorticoid. This can cause hypertension. However, it typically results in virilization of females due to the overproduction of androgens.
- **Option C: 3β-hydroxysteroid dehydrogenase (3β-HSD) deficiency** leads to impaired production of all classes of steroid hormones. This condition can result in a wide range of phenotypes but is less commonly associated with hypertension and the specific combination of male pseudohermaphroditism and hypertension.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl 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 pattern of steroidogenesis impairment. Recognizing this condition is critical for managing the patient's hypertension, electrolyte imbalance, and for gender assignment.

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