Multiple experimental/natural models (e.g.- hypophysectomised or pharmacological/immunological deprivation of GnRH, hpg mice or hypogonadal men), inactivating or hyper-activating mutations in FSH-R/LHCG-R in men, murine genetic KOs collectively show the crucial role of FSH and LH (via T) in spermatogenic development and maintenance. Here, PLOD1 is linked to hypogonadism.