GNRH1 and hypogonadotropic hypogonadism: Across the spectrum of pubertal disorders, altered neurotrophic signaling contributes to distinct clinical phenotypes, from premature activation of the HPG axis in central precocious puberty to impaired GnRH neuron development in congenital hypogonadotropic hypogonadism and reversible suppression of GnRH pulsatility in functional hypothalamic amenorrhea.