What is a defining characteristic of androgen insensitivity in a patient with primary amenorrhea?

Androgen insensitivity syndrome (AIS) is a condition that affects sexual development before birth and during puberty. It occurs due to mutations in the androgen receptor, which leads to an inability of the body to respond to androgens (male hormones). Individuals with complete androgen insensitivity usually present as females despite having a 46,XY karyotype. A defining characteristic of AIS, especially in individuals with primary amenorrhea, is the absence of a uterus but the presence of breast development.

In cases of complete AIS, the external genitalia develop along female lines, and secondary sexual characteristics such as breast development occur due to estrogen production. However, because the body cannot respond to testosterone, which would promote the development of male internal reproductive structures, the uterus is absent. This clinical presentation aligns with the answer choice indicating the absence of the uterus in the presence of breasts, emphasizing the unique hormonal environment and developmental outcomes in AIS.