**Question:** Commonest cause of female pseudohermaphroditism is:

**Core Concept:** Female pseudohermaphroditism is a condition where an individual with a female genetic makeup (XX karyotype) exhibits male physical characteristics (virilization) despite having a female genetic makeup. This can be due to hormonal imbalances or enzyme deficiencies affecting the production of sex hormones.

**Why the Correct Answer is Right:** The correct answer is "C. 46,XX Klinefelter syndrome." In this condition, males have an extra X chromosome (47,XXY) leading to hormonal imbalances and reduced production of estrogen and increased production of testosterone. The excess testosterone causes virilization in female pseudohermaphroditism cases.

**Why Each Wrong Option is Incorrect:**

A. 46,XX Turner syndrome: This is a condition with absence of one X chromosome (45,XX), resulting in reduced estrogen and increased progesterone levels, which does not explain the excess testosterone causing virilization in female pseudohermaphroditism.

B. 46,XX Rett syndrome: This is a neurodevelopmental disorder, not a hormonal disorder affecting sex hormone production in pseudohermaphroditism.

D. 46,XX Turner-Klinefelter syndrome: This is a combination of Turner and Klinefelter syndromes, which do not occur together and do not explain the virilization in female pseudohermaphroditism.

**Clinical Pearl:** Klinefelter syndrome is the most common cause of male infertility but can also present with pseudohermaphroditism due to hormonal imbalances.

**Correct Answer:** C. 46,XX Klinefelter syndrome