GH stimulation tests in adults with PWS have shown GH deficiency in 0–67% (2, 16, 18), but the GH deficiency is of hypothalamic origin and most GH stimulation tests stimulate the secretion of GH from the pituitary gland which may result in falsely normal GH responses (2, 16). Here, GH1 is linked to Prader-Willi syndrome.