USMLE (United States Medical Licensing Examination) Step 1 Practice Exam

Which condition is characterized by male internal genitalia but incompletely virilized external genitalia?

1. Klinefelter syndrome

2. Turner syndrome

3. Androgen insensitivity syndrome

4. True hermaphroditism

The correct answer is: Androgen insensitivity syndrome

Androgen insensitivity syndrome is the condition characterized by male internal genitalia paired with incompletely virilized external genitalia. It results from a genetic mutation affecting the androgen receptor, leading to resistance to male hormones (androgens) that are responsible for the development of male characteristics. In individuals with this syndrome, despite having XY chromosomes and functioning testes that produce testosterone, the lack of response to androgens prevents the typical masculinization of external genitalia. Thus, they often present with a female phenotype, such as the presence of breast development, but lack a uterus or normal female reproductive organs, making their external genitalia appear female or ambiguous. Understanding the context of this condition is crucial. Klinefelter syndrome involves the presence of an extra X chromosome in males, leading to tall stature, gynecomastia, and infertility, but does not result in external genitalia that are incompletely masculinized. Turner syndrome occurs in females with a complete or partial absence of one X chromosome and features development of female external genitalia and internal structures; it does not present with male genitalia. True hermaphroditism refers to a condition where both ovarian and testicular tissues are present, which may lead to a mixture of male and female