Growth hormone (GH) deficiency (GHD) is prominent in neuroendocrine dysfunctions of PWS and early GH therapy (GHT) is recommended.1,11,12 GHT hypersensitivity is likely in PWS, with a marked increase in insulin growth factor 1 (IGF1).13 GH binding proteins (GHBP) are potential regulators of the effect of GH and IGF1 under GHT. Here, IGF1 is linked to Prader-Willi syndrome.