PYY and Prader-Willi syndrome: There was a statistically significant increase in circulating levels of PYY at 30 and 60 min (vs 0 min after the breakfast, p < 0.01) and at 80, 100 and 160 min after non-palatable food in PWS patients administered with the breakfast + non-palatable session, whereas no such difference was found in those administered with the breakfast + chocolate session (intra-group analysis).