## **Core Concept**
The question pertains to the identification of the most common enzyme deficiency that leads to hypertension in children. This involves understanding the genetic and biochemical basis of hypertension, particularly in pediatric populations. The key concept here revolves around **steroid biosynthesis** and **mineralocorticoid regulation**.

## **Why the Correct Answer is Right**
The correct answer, **11β-hydroxylase deficiency**, is a form of congenital adrenal hyperplasia (CAH) that leads to an overproduction of **deoxycorticosterone (DOC)**, a potent mineralocorticoid. This results in **sodium retention**, **potassium excretion**, and **hypertension**. 11β-hydroxylase is crucial for converting **11-deoxycortisol** to **cortisol**. A deficiency in this enzyme leads to the accumulation of **11-deoxycortisol**, which has mineralocorticoid activity, thereby causing hypertension.

## **Why Each Wrong Option is Incorrect**
- **Option A:** **17α-hydroxylase deficiency** is another form of CAH that can lead to hypertension due to the overproduction of mineralocorticoids. However, it is less common than 11β-hydroxylase deficiency and typically presents with **hypokalemia** and **hypertension** but also **sexual infantilism** in males.
- **Option B:** **21-hydroxylase deficiency** is the most common cause of CAH but usually leads to **virilization** and **salt wasting** (in its classical form) rather than hypertension.
- **Option D:** While other enzyme deficiencies can lead to disturbances in steroid biosynthesis, **20,22-desmolase deficiency** is extremely rare and presents with **adrenal insufficiency** and **sexual infantilism**, not typically with hypertension as a primary feature.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that **11β-hydroxylase deficiency** accounts for about **5-8%** of CAH cases and is the second most common cause of CAH after **21-hydroxylase deficiency**. It is a critical diagnosis to consider in children presenting with **hypertension** and **virilization**.

## **Correct Answer:** . **11β-hydroxylase deficiency**