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

Which condition is characterized by insufficient conversion of testosterone to dihydrotestosterone?

1. Androgen insensitivity syndrome

2. Klinefelter syndrome

3. Precocious puberty

4. 5α-reductase deficiency

The correct answer is: 5α-reductase deficiency

The condition characterized by insufficient conversion of testosterone to dihydrotestosterone (DHT) is indeed related to 5α-reductase deficiency. Dihydrotestosterone is an androgen that is crucial for the development of male external genitalia and other male secondary sexual characteristics. In individuals with 5α-reductase deficiency, the enzyme responsible for converting testosterone into DHT is deficient or absent. This deficiency leads to ambiguous genitalia or underdeveloped male genitalia at birth, despite the presence of normal testosterone levels. As individuals with this condition grow, they may undergo some virilization during puberty due to increased levels of testosterone, but they might still present with atypical genital formations during early development. In contrast, other conditions listed do not directly relate to the conversion process of testosterone to DHT. For instance, androgen insensitivity syndrome involves a lack of response to androgens, including DHT, but does not specifically result from/affect the conversion process. Klinefelter syndrome is primarily associated with an extra X chromosome leading to hypogonadism and infertility, but it does not involve the conversion mechanism of testosterone to DHT. Precocious puberty refers to early sexual maturation and is not connected to the enzymatic