**Core Concept**
Adrenogenital syndrome, also known as Congenital Adrenal Hyperplasia (CAH), is a group of inherited disorders caused by the deficiency of enzymes involved in the biosynthesis of cortisol from cholesterol in the adrenal cortex. This deficiency leads to an accumulation of precursor hormones, which are then shunted towards the production of androgens, resulting in various clinical manifestations.

**Why the Correct Answer is Right**
The most common cause of CAH is a deficiency of the enzyme 21-hydroxylase, which is responsible for converting 17-hydroxyprogesterone to 11-deoxycortisol in the final step of cortisol production. This deficiency leads to an overproduction of androgens, such as dehydroepiandrosterone (DHEA) and androstenedione, resulting in virilization of female genitalia and other clinical features. The 21-hydroxylase enzyme is encoded by the CYP21A2 gene, and mutations in this gene are responsible for the majority of CAH cases.

**Why Each Wrong Option is Incorrect**
**Option A:** 17-hydroxylase deficiency is another cause of CAH, but it is much less common than 21-hydroxylase deficiency.
**Option B:** 11-hydroxylase deficiency is a rare cause of CAH, characterized by an overproduction of 11-deoxycortisol.
**Option C:** Aldosterone synthase deficiency is a rare cause of CAH, characterized by a deficiency of aldosterone production.

**Clinical Pearl / High-Yield Fact**
The most common presentation of CAH is ambiguous genitalia in newborn females, which can be a classic exam trap. A high index of suspicion and prompt genetic testing are essential for diagnosing CAH.

**Correct Answer: D. 21-hydroxylase deficiency**