For example, chronic undernutrition, high levels of energy expenditure, or stress will lead to disruption of the GnRH pulse generator, which results, sequentially, in 1) alterations in the pulsatile pattern of GnRH release, 2) decrease in gonadotropin secretion from the pituitary (hypogonadotropism), 3) reduction in release of ovarian estradiol and progesterone, 4) absence of cyclic growth of the endometrium, and 5) amenorrhea, i.e. the cessation of menstruation (45). This evidence concerns the gene GNRH1 and amenorrhea.