Spontaneous and provoked growth hormone (GH) secretion and insulin-like growth factor I (IFG-I) concentration in patients with beta thalassaemia and delayed growth

Abstract

Growth retardation in children with thalassaemia major is multifactorial. We studied the growth hormone (GH) response to provocation by clonidine and glucagon, measured the circulating concentrations of insulin, insulin-like growth factor-I (IGF-I), IFG-binding protein-3 (IGFBP3), and ferritin, and evaluated the spontaneous nocturnal (12 h) GH secretion in prepubertal patients with thalassaemia and age-matched children with constitutional short stature (CSS) (height SDS < -2, but normal GH response to provocation). The anatomy of the hypothalamic pituitary area was studied in patients with abnormal GH secretion using MRI scanning. Children with thalassaemia had significantly lower peak GH response to provocation by clonidine and glucagon (8.8 ± 2.3 μg/l and 8.2 ± 3.1 μg/l respectively) than did controls (17.6 ± 2.7 μg/l and 15.7 ± 3.7 μg/l respectively). They had significantly decreased circulating concentrations of IGF-I and IGFBP3 (68.5 ± 19 ng/ml and 1.22 ± 0.27 mg/l respectively) compared to controls (153 ± 42 ng/ml and 2.16 ± 0.37 mg/l respectively). Seven of the thalassaemic children had a GH peak response of < 7 μg/l after provocation. Those with a normal GH response after provocation also had significantly lower IGF-I and IGFBP3 concentrations than controls. Analysis of their spontaneous nocturnal GH secretion revealed lower mean (2.9 ± 1.77 μg/l) and integrated (2.53 ± 1.6 μg/l) concentrations compared to controls (4.9 ± 0.29 μg/l and 5.6 ± 0.52 μg/l respectively). Five of them had mean nocturnal GH concentration < 2 μg/l and four had maximum nocturnal peak below 10 μg/l. These data denoted defective spontaneous GH secretion in some of these patients. MRI studies revealed complete empty sella (n=2), marked diminution of the pituitary size (n=4), thinning of the pituitary stalk (n=3) with its posterior displacement (n=2), and evidence of iron deposition in the pituitary gland and midbrain (n=7) in those patients with defective GH secretion (n=9). Serum ferritin concentration was correlated significantly with the circulating IGF-I (r=-0.47, pr=-0.43), p<0.01) concentrations. These data prove a high prevalence of defective GH secretion in thalassaemic children associated with structural abnormality of their pituitary gland.