In humans, hyperprolactinaemia is associated with a marked reduction in both the frequency and amplitude of LH pulses (Bohnet et al. 1976, Matsuzaki et al. 1994) indicative of a change in GnRH pulses, and the suppression of LH pulsatility can be reversed by reducing serum prolactin concentrations to normal (Moult et al. 1982). This evidence concerns the gene PLOD1 and Increased circulating prolactin concentration.