An 8 days old male infant is brought to the emergency depament with vomiting, lethargy, dehydration and features of shock. Clinical examination reveals hyper pigmentation of the genital skin and normal external genitalia. Abdominal examination is unremarkable. Blood tests revealed sodium of 124 meq/1, potassium of 7 meq/1 and hypoglycemia. Which of the following is the most likely diagnosis:

**Core Concept**
The underlying principle being tested involves **congenital adrenal hyperplasia (CAH)**, a group of autosomal recessive disorders affecting the **adrenal glands**. This condition leads to impaired production of **corticosteroids** and **aldosterone**, while simultaneously causing an overproduction of **androgens**.

**Why the Correct Answer is Right**
The correct answer is related to CAH, specifically the **salt-wasting form** of 21-hydroxylase deficiency. This condition is characterized by a deficiency of the **21-hydroxylase enzyme**, leading to decreased production of **aldosterone** and **cortisol**, and increased production of **androgens**. The clinical presentation of vomiting, lethargy, dehydration, and shock, along with hyperpigmentation of the genital skin, hypoglycemia, hyponatremia, and hyperkalemia, is consistent with this diagnosis.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because it does not specify the underlying enzyme deficiency.
**Option B:** Incorrect as it may not present with the same severity of salt-wasting and shock.
**Option C:** Incorrect because it is not directly related to the clinical presentation described.
**Option D:** Incorrect as it does not account for the androgen excess and adrenal crisis.

**Clinical Pearl / High-Yield Fact**
In cases of CAH, particularly the salt-wasting form, it is crucial to recognize the signs of adrenal crisis, including dehydration, shock, and electrolyte imbalances, and to initiate prompt treatment with **glucocorticoids** and **mineralocorticoids**.

**Correct Answer:** D. Congenital Adrenal Hyperplasia

✓ Correct Answer: A. Congenital Adrenal Hyperplasia (CAH)