The Testis in Childhood Between Birth and Puberty

Abstract

The testis of newborns and young infants is quite active endocrinologically [1, 2]. Serum levels of gonadotropins, testosterone, insulin-like factor 3 (INSL3), and inhibin B peak around age 2–3 months, when testosterone is close to a lower adult level [1, 3]. Despite this pronounced androgen activity in early infancy, the absence of expression of androgen receptors in Sertoli cells renders them unresponsive and prevents maturation of the testis [4]. In general, the histology of the infantile testis is similar to that of the third-trimester fetal testis. Leydig cells are noticeable during the postnatal hormone peak. The seminiferous tubules contain infantile spermatogonia and undifferentiated Sertoli cells, which produce large amounts of anti-Müllerian hormone (AMH) and inhibin B [1, 4, 5]. Both types of cells increase in number during the first 3 months of life [6, 7]. Occasionally, a few gonocyte-like cells may be seen during the first few months after birth. These cells express some of the embryonic germ cell markers (e.g., placental-like alkaline phosphatase [PLAP], M2A/D2-40) and pluripotency markers, such as OCT4, NANOG, and AP2γ, although the expression is often weak compared with early fetal gonocytes [8, 9].