Children with hyperphagia and obesity of Prader-Willi syndrome (PWS) have previously been shown to have blunted pancreatic polypeptide (PP) response to low protein meal stimulation. To evaluate the effects of various protein challenges on PP release in children with PWS, we administered both a low protein (0.2 g/kg) and a high protein (2.0 g/kg) meal stimulation test to 12 children previously diagnosed as having PWS and to an age- and weight-matched group of 19 obese but otherwise normal children. Serum samples were collected just before and for 3 h after meal ingestion. The mean (+/- SD) age was 11.7 +/- 4.2 yr for the PWS group and 10.3 +/- 3.8 yr for the obese group (P = 0.323). The percent ideal body weight for height for the PWS group (mean +/- SD 186 +/- 48%) was not significantly different from the percent ideal body weight for height for the obese group (174 +/- 35%; P = 0.421). Peak PP responses were significantly less for the PWS group than for the obese group for both the low and high protein meal stimulations. The mean (+/- SE) peak PP response with the low protein meal was 76.1 +/- 13 pg/ml for the PWS group and 302 +/- 93 pg/ml for the obese group (P less than 0.05). The mean peak response with the high protein meal was 181 +/- 51 pg/ml for the PWS group and 581 +/- 127 pg/ml for the obese group (P less than 0.01). Glucose rises were similar for both tests, although the PWS group did have a slightly smaller rise in glucose after the low protein stimulation than was observed in the obese group. The insulin response was also significantly less for the low protein meal in the PWS group compared to the low protein insulin response of the obese group. There were no significant differences in the insulin responses observed in both groups with the high protein meal test. This study confirms our previous observation and suggests that many children with PWS have a functional deficiency of PP. Our current study demonstrates that this condition is not a result of their obese condition or an alteration in their response threshold to protein.

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