The growth hormone-insulin-like growth factor axis in adult patients with Prader Willi syndrome.

Abstract

Prader Willi syndrome (PWS) is a genetic disorder characterised by short stature, extreme obesity, body composition abnormalities and behavioural problems. Hypothalamic dysfunction with low growth hormone (GH) secretion and low levels of GH-related growth factors is common. However, the interpretation is difficult because of the concomitant obesity, which in itself has important effects on the GH-IGF-I-system. We therefore analysed free and total IGF-I, total IGF-II and their binding proteins in obese PWS adults before and during 12 months GH treatment. Seventeen adults, 9 men and 8 women, 17-32 years of age with a mean BMI of 35+/-2.3 kg/m(2) participated. All had clinical PWS. They were randomized to treatment with placebo or GH (Genotropin, Pharmacia) 0.8 IU (0.26 mg) for one month, and then 1.6 IU (0.53 mg) for 5 months. Subsequently GH doses were individually titrated to normal levels for age. Overnight fasting levels of free and total IGF-I, total IGF-II, GH-binding protein (GHBP) and IGF-binding proteins (IGFBP)-1, -2 and -3 were measured by RIA at baseline and after 6 and 12 months GH treatment. Mean levels+/-SEM of free IGF-I were 1.02+/-0.12 microg/L as compared to a reference value of 0.95+/-0.15 microg/L, while mean total IGF-I was 128+/-15 microg/L (212+/-14 microg/L) and total IGF-II was 704+/-45 microg/L (825+/-34 microg/L). Mean IGFBP-2 158+/-24 microg/L (764+/-72 microg/L) and GHBP 2.65 nmol/L (1.71+/-0.3 1nmol/L). IGFBP-1 and IGFBP-3 levels were normal. Both free and total IGF-I increased significantly during GH treatment, while IGF- and GH-binding proteins as well as total IGF-II remained unchanged. Low total IGF-I and, in relation to the obesity, low free IGF-I, low total IGF-II and non-suppressed IGFBP-1 are consistent with the concept that PWS patients have a partial GH deficiency, which can be corrected by GH replacement.