['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.', '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.', '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).'] Is testosterone enanthate therapy effective and independent of SRD5A2 and AR gene polymorphisms in boys with micropenis?