A baby girl with ambiguous genitalia is found to have 21-hydroxylase deficiency of the salt-wasting type.Which of the following karyotypes would you expect to find?
**Core Concept**
The question is testing the understanding of the relationship between congenital adrenal hyperplasia (CAH), specifically 21-hydroxylase deficiency, and its association with sex chromosomes. **21-hydroxylase deficiency** is a form of CAH that leads to an overproduction of androgens, causing virilization of female genitalia.
**Why the Correct Answer is Right**
The **salt-wasting type** of CAH is characterized by a deficiency of aldosterone, leading to excessive loss of sodium and water, resulting in dehydration and shock. This condition is most commonly associated with **46,XX karyotype**, where the individual has two X chromosomes but a deficiency in the 21-hydroxylase enzyme, leading to androgen excess and virilization of female genitalia. The excess androgen production in females with 21-hydroxylase deficiency causes the development of ambiguous genitalia, which is a hallmark of this condition.
**Why Each Wrong Option is Incorrect**
**Option A:** 46,XY karyotype is incorrect because it is associated with androgen insensitivity syndrome (AIS) or 5-alpha-reductase deficiency, not 21-hydroxylase deficiency.
**Option B:** 47,XXY karyotype is incorrect because it is associated with Klinefelter syndrome, a condition characterized by tall stature, infertility, and other features, not 21-hydroxylase deficiency.
**Option C:** 45,XO karyotype is incorrect because it is associated with Turner syndrome, a condition characterized by short stature, infertility, and other features, not 21-hydroxylase deficiency.
**Clinical Pearl / High-Yield Fact**
In infants with ambiguous genitalia, it is essential to perform a karyotype analysis to determine the presence of 46,XX or 46,XY karyotype, as this will guide the diagnosis and management of the condition. A 46,XX karyotype with 21-hydroxylase deficiency is a classic association that should be considered in infants with virilized genitalia.
**Correct Answer:** . **46,XX**.