2019 年 66 巻 9 号 p. 837-842
Steroid 5α-reductase type 2 deficiency (5αRD2) is a congenital disorder of sex development caused by impairment of conversion from testosterone (T) to 5α-dihydrotestosterone (DHT). DHT deficiency leads to various degrees of undervirilized external genitalia including micropenis, primarily correlated with mutations of the SRD5A2 gene that encodes 5α-reductase type 2. Four Japanese boys with isolated micropenis were diagnosed as 5αRD2 by elevated ratios of serum T/DHT, and decreased ratios of urinary 5α/5β-reduced steroid metabolites. Genetic analyses for SRD5A2 identified that the four patients shared a hypomorphic mutation R227Q that has a residual activity related to the mild-form of 5αRD2. For prepubertal micropenis, DHT was transdermally applied to the four patients at the ages of 4–11 year, increasing a median of stretched penile lengths (SPLs) from 2.6 cm (–2.5 SD) to 4.4 cm (–0.2 SD). Nevertheless, the post-pubertal penile growth was apparently retarded, despite normal levels of T secreted from well-developed testes. The second course of DHT treatment underwent at ages of 12–18 year, but unable to normalize SPLs at a range of 6.0 to 7.0 cm (–3.4 to –2.4 SD). The prostate volumes of two patients were variable at 8.1 and 21 cm3, and a sperm cell count of one patient was normal as young adult. DHT treatment contributes to development of the penis and prostate, which are favorable for the potential fertility of 5αRD2 adults. Meanwhile, the retarded penile growth and a risk of prostate overgrowth may complicate the post-pubertal management with DHT for 5αRD2 males.
