[Changes in carbohydrate metabolism and insulin resistance in patients with Prader-Willi Syndrome (PWS) under growth hormone therapy].

BACKGROUND: Life expectance and life quality have markedly changed in PWS patients within the last 10-15 years. A strict diet, improved physical activity and an additive growth hormone treatment have led to these changes. Growth hormone therapy decreases body fat and improves final height. But growth hormone also antagonizes insulin and therefore increases the diabetic potential. The purpose of our study was to investigate incidence and multiple dependencies of development of impaired carbohydrate metabolism in patients with PWS under growth hormone therapy and to determine suitable parameters for the work-up. PATIENTS AND METHODS: 34 patients with genetically approved PWS have been treated with growth hormone for at least 0.5 years. The mean duration of growth hormone treatment was 2.15 years (0.5-4.51). At the start of growth hormone treatment patients were 1.33 to 16.47 years old. The clinical picture and the nutritional situation of children with PWS change age-dependent and can be divided up into three phases. The patients were duty subdivided into three age-groups at the beginning of growth hormone treatment. Group 1: 15 PWS patients, mean age 2.62 years (1.33-3.78). Group 2: 10 PWS patients, mean age 5.54 years (4.08-7.61). Group 3: 9 PWS patients, mean age 11.35 years (8.89-16.47). Data were collected within 0.3-0.38 years before start of treatment and every 6 months throughout the treatment period. Anthropometrical data, fat mass by bioelectric impedance analysis (BIA), fasting insulin, HbA1c, C-peptide, blood fats and the blood sugar profile in oral glucose tolerance tests (OGT/1.75 g glucose/kg body mass) were obtained. Growth hormone therapy was started with an average dose of 0.031 mg/kg body mass in all groups. Insulin resistance was based on Homeostasis Model Assessment-Test (HOMA). RESULT: No IR or pathological OGT were detected when growth hormone therapy started before the 4th year of life. When therapy started between the 4th and 8th year, PWS patients with normal weight did not develop an IR under GH therapy. 6% developed a glucose tolerance (IGT) disorder and 4% developed an increased fasting glucose (IFG). 5 of 9 PWS patients older than 8 years at therapystart showed a transient disorder of glucose metabolism: 11% of the results obtained in these patients presented an IR with no pathological OGT, 13% showed an IR with IGT, 7% showed an IR with IFG, and 2% showed an IR with transient diabetes. For 4% the IFG persisted with no IR, for 4% the IGT persisted with no IR. These patients differed from younger ones by an increased average BMI, an increase fat body ratio and an increase fasting insulin as well as an already reached puberty. No difference was found in C-peptide, HbA1c or GH dose/kg/body mass.
CONCLUSION: Transient glucose metabolism disorders with no development of manifest insulin resistance are shown by PWS patients with normal weight starting from 4th year under GH therapy. Changes in the glucose metabolism with and with no development of IR appear after start of puberty and weight increase. Changes persisted partially for 18 months. GH therapy was not interrupted for any patient, whereby physical training and dietetic measurements were increased for all patients. HOMA-index and OGT shall be used in parallel to monitor glucose metabolism as both show independently distinctive features. HbA1c and C-peptide are not suitable parameters for monitoring carbohydrate metabolism in PWS patients under GH treatment.