Characteristics of the eating disorder in Prader-Willi syndrome: implications for treatment.

Over-eating and resultant obesity is well recognized as a central feature of the Prader-Willi Syndrome (PWS). The eating behaviour of 13 subjects with PWS was been studied retrospectively over a 28-day period and also by direct observation when given free access to food. Changing cognitions normally associated with food intake (e.g. changes in hunger) were assessed using visual analogue scales (VAS) and by asking subjects to rate photographs of particular foods. Eight out of 13 subjects (61%) with PWS had to have their access to food severely restricted. Ten (77%) ate excessive amounts when given free access to food, and although feelings of 'hunger', 'desire to eat' and 'fullness' changed in the expected direction, these changes were delayed, compared to a control group, and only occurred after eating a significantly greater amount of food. Ratings of 'hunger' and 'fullness' started to return to pre-meal levels sooner than in the controls. The present authors consider that PWS is an example of genetic obesity secondary to an impaired satiety response. These observations have important implications for treatment.

Measurement of excessive appetite and metabolic changes in Prader-Willi syndrome.

The behavioural, cognitive and metabolic response to food intake was studied in 13 adults with the Prader-Willi syndrome (PWS) and compared to ten age-matched controls. Rates of eating were observed during one hour's access to food and feelings of hunger were assessed using a visual analogue scale. Blood was taken for estimation of glucose, insulin, cholecystokinin (CCK), prolactin, growth hormone (GH) and cortisol every 20 min for a total period of 100 min. Ten (76%) of the subjects with PWS ate steadily for the whole hour that food was available and on average consumed three times more calories than the control group. The median ratings for feelings of hunger in the PWS group changed in the expected direction but these changes were delayed compared to the control group and only reached the same level as the controls after the PWS subjects had eaten a significantly greater amount of food. In the PWS group, in contrast to the control group, feelings of hunger started to re-emerge shortly after food was removed. There were marked differences between individuals with PWS in the extent of the changes in serum prolactin levels. Increases in plasma glucose levels were inversely correlated with changes in hunger ratings in the PWS group, but not the control group. There was a significantly greater increase in serum CCK levels during the meal in the PWS group than in the control group indicating that in PWS failure of peripheral release of CCK in response to food intake was not the explanation for the impaired satiety response.