What is the presentation of 5-alpha reductase deficiency?

• A. Inability to produce testosterone
• B. Male internal genitalia with ambiguous external genitalia
• C. Female internal genitalia with male external genitalia
• D. Complete androgen insensitivity

Answer: (B)

The correct presentation of 5-alpha reductase deficiency is characterized by male internal genitalia with ambiguous external genitalia. This condition is due to a genetic mutation that impairs the conversion of testosterone into dihydrotestosterone (DHT), a more potent androgen necessary for the development of male external genitalia.

Typically, 5-alpha reductase deficiency is identified at birth or during puberty when male genitalia development does not align with the expected male phenotype. Individuals typically have normal male internal structures, including testes and often a prostate, but the external genitalia may appear ambiguous. This can manifest as a small penis, a hypospadias-like condition, or even a clitoromegaly due to insufficient DHT during critical periods of sexual differentiation in utero.

In summary, the defining feature of this condition lies in the presence of male internal genitalia alongside the atypical external genital development, which reflects the role of DHT in the male sex differentiation process.