Testosterone treatment for micropenis in partial androgen insensitivity syndrome.

The optimal approach to hormonal treatment aimed at increasing penis size has been established for infant males with micropenis; however, data are limited in partial androgen insensitivity syndrome (PAIS). We report a 6-month-old male patient treated with intramuscular testosterone for micropenis. At birth, he presented with atypical genitalia, including a microphallus, hypospadias, and a bifid scrotum. His karyotype was 46,XY, and endocrine evaluation revealed normal testicular function. A novel missense variant of the AR gene (p.G578E) was identified. Intramuscular testosterone enanthate 62.5 mg/dose was administered every 4 weeks for 3 doses (6-8 months). Stretched penile length increased from 18 to 30 mm (+67%) without adverse events. During treatment, luteinizing hormone secretion was suppressed, with trough levels falling below the limit of detection, consistent with androgen-mediated negative feedback. Luteinizing hormone levels during mini-puberty in response to testosterone treatment, supporting testosterone therapy in patients with PAIS.