A full-term newborn has ambiguous genitalia. Ultrasonographic examination shows a uterus and bilateral uterine tubes. Chromosomal analysis shows a 46,XX karyotype. Which of the following most likely occurred during development?

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Deficient activity of 21-hydroxylase in the adrenal cortex leads to congenital adrenal hyperplasia, causing excess androgen production and resulting in virilization of a 46,XX individual, leading to ambiguous genitalia.  CYP21A2 (21-hydroxylase) deficiency is the most common enzyme defect in the adrenal gland. The lack of 21-hydroxylase leads to decreased cortisol synthesis. By feedback regulation, low serum cortisol concentration results in increased production of ACTH. Increased ACTH leads to adrenal gland hyperstimulation and increased production of adrenal androgens during fetal development which results abnormal gonadal development. Females with this form of the disease present at birth due to ambiguity in the external genitalia.

A Full-Term Newborn Has Ambiguous Genitalia