Commonest cause of female pseudohermaphrodism –
**Core Concept**
Female pseudohermaphroditism, also known as female external genitalia with virilization, is a condition where an individual is genetically female (46,XX) but has some degree of virilization of the external genitalia. This condition is usually caused by excess androgen exposure during fetal development.
**Why the Correct Answer is Right**
The commonest cause of female pseudohermaphroditism is congenital adrenal hyperplasia (CAH), specifically the 21-hydroxylase deficiency. This enzyme deficiency leads to an accumulation of 17-hydroxyprogesterone, which is then shunted to androgen production, resulting in excess androgen exposure to the fetus. This excess androgen causes virilization of the external genitalia in females.
**Why Each Wrong Option is Incorrect**
* **Option A:** Congenital syphilis is a rare cause of female pseudohermaphroditism, typically associated with other systemic symptoms.
* **Option B:** Androgen insensitivity syndrome is a condition where individuals have a functional androgen receptor but are resistant to its effects; it is not a cause of excess androgen exposure.
* **Option C:** Maternal androgen exposure due to conditions like polycystic ovary syndrome (PCOS) is not a common cause of female pseudohermaphroditism.
**Clinical Pearl / High-Yield Fact**
The classic presentation of CAH includes ambiguous genitalia, early onset of pubic hair, and precocious puberty in females.
**Correct Answer:** C.