A baby girl born 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 in this baby?
**Core Concept:** 21-hydroxylase deficiency is a genetic disorder affecting the adrenal glands, specifically the CYP21A2 gene on chromosome 6. In the salt-wasting type, excess cortisol and aldosterone are produced, leading to hyponatremia, hypokalemia, and hyperkalemic hypovolemic shock.
**Why the Correct Answer is Right:** The correct answer, karyotype D (46, XY), describes a male karyotype with two X chromosomes (46) and a single Y chromosome (XY). In this case, the baby has a normal male karyotype, which is consistent with a 21-hydroxylase deficiency in a male. The salt-wasting form of the disease is more common in males due to the higher activity of the steroidogenic enzymes.
**Why Each Wrong Option is Incorrect:**
A. Female karyotype (45, X) would indicate Turner syndrome, which has no association with 21-hydroxylase deficiency.
B. Female karyotype (46, XX) would indicate a non-male karyotype, which is not consistent with the male-predominant presentation of the salt-wasting form of 21-hydroxylase deficiency.
C. Male karyotype (46, XY) would indicate a normal karyotype, but this option is incorrect because the salt-wasting form of 21-hydroxylase deficiency is more common in females, not males, and does not explain the male presentation in the question.
**Clinical Pearl:** In cases of ambiguous genitalia and suspected 21-hydroxylase deficiency, a karyotype analysis is essential to determine the sex of the affected individual. This can guide the appropriate management and prognosis for the child and its family.
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**Core Concept:** Karyotype analysis is a test that examines the chromosomes in a cell to identify genetic disorders. It involves staining and examining the chromosomes under a microscope to determine the number and types of chromosomes present.
**Why the Correct Answer is Right:** Karyotype D (46, XY) is correct because the baby has a male karyotype, which indicates that the patient is a male with a genetic abnormality causing ambiguous genitalia, such as 21-hydroxylase deficiency. This deficiency leads to a male presentation due to the higher activity of androgen-producing enzymes in males compared to females.
**Why Each Wrong Option is Incorrect:**
A. Female karyotype (45, X) would indicate Turner syndrome, a genetic disorder characterized by partial or complete absence of one X chromosome. This is not the correct explanation for the male presentation in ambiguous genitalia cases.
B. Male karyotype (46, XY) would indicate a normal karyotype and is incorrect as the deficiency is causing ambiguous genitalia in a male.
C. Female karyotype (46, XX) would indicate a normal karyotype and is incorrect as the deficiency is causing ambiguous genitalia in a male.