## **Core Concept**
The patient's presentation of primary amenorrhea, well-developed breasts, and scanty axillary and pubic hair, along with the absence of the uterus and vagina on ultrasonography, suggests a condition affecting both the development of the reproductive system and secondary sexual characteristics. This points towards a disorder of sex development (DSD), specifically Androgen Insensitivity Syndrome (AIS) or a condition affecting Müllerian duct development.

## **Why the Correct Answer is Right**
The correct answer, **46,XY**, is associated with Androgen Insensitivity Syndrome (AIS). In AIS, individuals have a 46,XY genotype, which leads to the production of testes and consequently, the production of anti-Müllerian hormone (AMH). AMH causes the regression of Müllerian ducts, resulting in the absence of the uterus, fallopian tubes, and upper part of the vagina. The presence of testes also leads to the production of androgens. However, due to the androgen receptor insensitivity, the individual does not respond to androgens, leading to a lack of development of male external genitalia and secondary sexual characteristics like axillary and pubic hair. The breasts develop due to the peripheral conversion of androgens to estrogens.

## **Why Each Wrong Option is Incorrect**
- **Option A: 45,X** - This genotype is associated with Turner syndrome, characterized by short stature, gonadal dysgenesis, and a lack of breast development, which does not match the patient's presentation of well-developed breasts.
- **Option B: 46,XX** - This genotype is typical for females. Individuals with a 46,XX genotype and Müllerian duct abnormalities (like Mayer-Rokitansky-Küster-Hauser syndrome) would have a normal development of secondary sexual characteristics and absence of the uterus and vagina but would not explain the scanty axillary and pubic hair.
- **Option D: 47,XXY** - This genotype is associated with Klinefelter syndrome, characterized by male hypogonadism, infertility, and usually, a lack of gynecomastia or presence of female breast tissue.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that in cases of Androgen Insensitivity Syndrome (AIS), patients often present with primary amenorrhea, female external genitalia, well-developed breasts, and little to no axillary and pubic hair, along with the absence of the uterus and vagina. The condition is an important consideration in the differential diagnosis of disorders of sex development.

## **Correct Answer: . 46,XY**