Testosterone enanthate therapy is effective and independent of SRD5A2 and AR gene polymorphisms in boys with micropenis

Purpose: We report penile length (PL) responses to testosterone enanthate (TE) therapy for micropenis, and the relevance of the V89L polymorphism of SRD5A2 encoding the 5alpha-reductase type 2 and CAG repeat length polymorphism of AR encoding the androgen receptor. Materials and Methods: A total of 53 Japanese boys with micropenis (less than -2.0 SD) 0 to 13 years old who had no SRD5A2 or AR mutation were examined. TE was given at a dosage of 25 mg intramuscularly, and PL was measured at least 4 weeks after the injection. The 2 polymorphisms were determined by direct sequencing. Results: PLs became -2.0 SD or greater in all the boys after TE therapy (1 injection in 4 boys, 2 in 28, 3 in 19 and 4 in 2), with a significant increase in the medians of PLs (from 2.5 to 3.5 cm, p <0.0001) and SD score, (from -2.6 to -0.7, p <0.0001). The increment in actual PL at the first injection ranged from 0.2 to 1.5 cm (median 0.6) and was independent of age (r = 0.22, p = 0.12) and body surface area (r = 0.11, p =0.43), while that in PL SD score at the first injection ranged from 0.3 to 2.5 (1.0) and was inversely correlated with age (r = -0.33, p = 0.02) and body surface area (r = -0.37, p = 0.008). The actual PL increment at the first injection was also unrelated to initial PL (r = -0.03, p = 0.81). The median of actual PL increments at the first injection was similar among boys with V/V, V/L and L/L genotypes of SRD5A2 (0.6 cm in 18, 0.7 cm in 30 and 0.5 cm in 5, respectively, p = 0.77), and between boys with and without long CAG repeats (26 or greater) of AR (0.65 cm in 6 and 0.6 cm in 47, respectively, p = 0.77). In addition, there was no significant correlation between actual PL increment at the first injection and CAG repeat length (r = 0.06, p = 0.67). Conclusions: Our results suggest that administration of 25 mg TE is effective for micropenis in prepubertal boys with no SRD5A2 or AR mutation, with variable but significant PL increments, and that the penile responsiveness to TE therapy is independent of the V89L and the CAG repeat length polymorphisms.