When Stat5b, a downstream effector of the GH receptor (GHR), was ablated in mice, body weights and bone lengths were reduced in a manner similar to Ames and Snell dwarf mice, although this effect was mainly apparent in male mice.(9) The defects of Snell and Ames dwarf as well as Stat5b−/− mice resulted in blunted GHR activity and are similar to the clinical characteristics of Laron syndrome in humans, where the GHR is mutated. Here, STAT5B is linked to Laron syndrome.