A 15-year-old female presents with primary amenorrhea. Her breasts are normally developed but she has no axillary or public hair The most likely diagnosis is
**Core Concept**
Primary amenorrhea refers to the failure to initiate menstruation by the age of 15 in individuals with normal secondary sexual characteristics, or by the age of 13 in those with delayed puberty. This condition can be caused by a variety of factors, including genetic, anatomical, and hormonal abnormalities.
**Why the Correct Answer is Right**
The presence of normally developed breasts (indicative of adequate estrogen levels) but absence of axillary and pubic hair (indicative of inadequate androgen levels) suggests a disorder of sex development with a deficiency in androgen secretion. This is characteristic of Androgen Insensitivity Syndrome (AIS), a genetic condition where the individual has a 46,XY karyotype but is resistant to androgens due to mutations in the androgen receptor gene. As a result, the individual develops female external genitalia despite having testes that produce androgens.
**Why Each Wrong Option is Incorrect**
**Option A:** Turner syndrome is characterized by a 45,X karyotype and short stature, which is not evident in this patient.
**Option B:** Congenital adrenal hyperplasia (CAH) typically presents with ambiguous genitalia and salt wasting in infancy, and does not typically result in a lack of pubic and axillary hair.
**Option C:** Mayer-Rokitansky-Küster-Hauser (MRKH) syndrome is characterized by the absence of the upper two-thirds of the vagina and uterus, but not typically by a lack of axillary and pubic hair.
**Clinical Pearl / High-Yield Fact**
Androgen Insensitivity Syndrome (AIS) is a classic example of a disorder of sex development where the individual's genetic sex (XY) does not match their phenotypic sex (female). This highlights the importance of considering both genetic and phenotypic characteristics when evaluating patients with primary amenorrhea.
**Correct Answer: D. Androgen Insensitivity Syndrome**