THE TIMING OF PUBERTY: WELL-KNOWN AND NEW ISSUES

Puberty is an important developmental milestone. It can be considered as a complex sequence of biological  events leading to progressive maturation of sexual characteristics ultimately leading to attainment of full  reproductive capacity. The decline in age at puberty in the general population has been paralleled by an increase  in the number of girls referred for evaluation of precocious puberty (PP). The recent pubertal trends have resulted in a concomitant lowering of the lower limit of normality of the pubertal onset. However, evidence suggests that  age at the gonadotropin and sex steroid surges have not changed. Thus, it looks as if an increasing proportion of  contemporary early pubertal girls may experience isolated gonadotropinindependent thelarche rather than central  PP, which may not be discernible on pubertal examination alone. Thus, the population-based limits of normality  srapid progressive PP as well as intracranial and other underlying pathology. The initiation of mammalian puberty  requires an increased pulsatile release of gonadotropin-releasing hormone (GnRH) from the hypothalamus. This  increase is brought about by changes in transsynaptic and glial-neuronal communication. Coordination of these  cellular interactions likely requires the participation of sets of genes hierarchically arranged within functionally  connected networks. The role of kisspeptins in the control of GnRH neurons and the transmission of the regulatory  actions of key signals, such as sex steroids, metabolic hormones and environmental cues, has been recently  studied, point out that the Kiss1 system is an indispensable player of the brain sexual differentiation during early  periods of maturation and the timing of puberty onset.