Previous in vitro studies of the Pro269Leu PRLR variant identified in a compound heterozygote individual with hyperprolactinaemia showed that the variant impaired STAT5 phosphorylation but had no effect on STAT5 signalling when expressed with WT PRLR (Kobayashi et al. 2018). The gene discussed is PRLR; the disease is hyperprolactinemia.