IGF1 and Prader-Willi syndrome: We first confirmed the high GH sensitivity of PWS patients, with IGF1 levels increasing fourfold after one year of treatment as ng/ml (50.3 ng/ml, ±34.4 vs. 184.5 ng/ml ± 93.8, P < 0.0001) and SDS (−0.92 ± 0.8 vs. 1.5 ± 1.04, P < 0.0001) (Table 1 and Fig. 1a).