GROWTH-HORMONE (GH) RESPONSE TO COMBINED PYRIDOSTIGMINE AND GH-RELEASING HORMONE ADMINISTRATION IN PATIENTS WITH PRADER-LABHARD-WILLI SYNDROME

We evaluated the GH response to combined administration of pyridostigmine (PD), a cholinergic agonist, and GH-releasing hormone (GHRH) (60 mg PD given orally 60 min before the GHRH bolus) as well as baseline IGF-I concentrations in 10 patients (5 males and 5 females, age 6.0-24 years) with Prader-Labhard-Willi (PLW) syndrome, 8 prepubertal obese children (4 males and 4 females, age 5.6-12.0 years) and 9 prepubertal short normal children (7 males and 2 females, age 8.0-12.8 years). Mean GH responses to PD + GHRH were significantly lower (p < 0.0001) in the PLW patients (13.8 +/- 3.3 mug/l) than in the short normal children (52.2 +/- 9.0 mug/l) and similar to those of the obese children (14.3 +/- 3.2 mug/l). Mean serum IGF-I levels were significantly lower (p < 0.05) in the PLW patients (117.5 +/- 26.4 mug/l) than in the obese (329.3 +/- 88.0 mug/l) and the short normal children (214.3 +/- 38.3 mug/l). Two of the PLW patients had absent GH responses to PD + GHRH associated with subnormal IGF-I concentrations, indicating pituitary GH deficiency. When these 2 cases were excluded from the statistical calculation, mean peak GH responses to PD + GHRH remained significantly lower (p < 0.0001) in the PLW patients (17.1 +/- 3.0 mug/l), while their mean serum IGF-I concentrations (143.4 +/- 71.5 mug/l) were not significantly different from those of the other two groups. These results indicate that patients with the PLW syndrome have a reduced or absent GH secretory reserve associated in some cases with low levels of IGF-I. Whether these findings are involved in the pathogenesis of their short stature remains to be confirmed.