A 15-day-old male neonate presented with failure to thrive, recurrent vomiting and symptoms of shock. On examination, severe dehydration is noted. He has normal genitalia along with precocious development of pubic hair, phallic enlargement and accelerated skeletal maturation. BP of the child was normal. Lab findings revealed hyponatremia and hypokalemia, increased serum 17 -hydroxyprogesterone and increased urinary pregnanetriol. A biopsy from the adrenal gland was taken. Which of the following is the most likely enzyme deficiency in the above patient: –

**Core Concept**
The patient presents with symptoms of congenital adrenal hyperplasia (CAH), a group of autosomal recessive disorders characterized by impaired steroidogenesis due to enzyme deficiencies in the adrenal glands. This leads to an accumulation of precursor hormones, which are then shunted towards alternative pathways, resulting in the production of excessive amounts of androgens.

**Why the Correct Answer is Right**
The patient's clinical presentation, including precocious puberty, failure to thrive, and electrolyte imbalances, suggests a deficiency in the enzyme 21-hydroxylase. This enzyme is crucial in the conversion of 17-hydroxyprogesterone to 11-deoxycortisol in the cortisol synthesis pathway. In its absence, the accumulated 17-hydroxyprogesterone is shunted towards the androgen synthesis pathway, leading to the production of excessive androgens. The increased levels of 17-hydroxyprogesterone and urinary pregnanetriol are consistent with this diagnosis. The biopsy from the adrenal gland would likely show hyperplasia of the adrenal glands due to the increased production of ACTH in response to the deficiency.

**Why Each Wrong Option is Incorrect**
* **Option A:** 11-beta-hydroxylase deficiency is another cause of CAH, but it is characterized by hypertension, not hypotension, and would not lead to the same pattern of electrolyte imbalances.
* **Option B:** 3-beta-hydroxysteroid dehydrogenase (3-beta-HSD) deficiency is a rare cause of CAH, but it would lead to a more generalized impairment of steroidogenesis, including the production of cortisol and aldosterone, which is not consistent with the patient's normal blood pressure.
* **Option D:** 17-alpha-hydroxylase deficiency is a rare cause of CAH, but it would lead to an inability to produce cortisol and androgens, resulting in hypogonadism and normal blood pressure, which is not consistent with the patient's clinical presentation.

**Clinical Pearl / High-Yield Fact**
The diagnosis of 21-hydroxylase deficiency can be confirmed by demonstrating a deficiency of this enzyme in the adrenal glands, either through genetic testing or enzyme assay. This condition is the most common cause of CAH and accounts for approximately 90% of cases.

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

✓ Correct Answer: A. 21-hydroxylase deficiency