Growth deficiency in polytransfused beta-thalassaemia patients is not growth hormone dependent

Growth deficiency is commonly seen in polytransfused beta-thalassaemia patients, especially in adolescence. It is not completely dependent on the lack of their pubertal growth spurt. GH impairment at different levels (hypothalamic or pituitary) and/or a reduced IGF-1 synthesis have been suggested the main causes of stunted growth in these patients. We evaluated the relationship between GH reserve and growth in short beta-thalassaemia patients.

Twenty-nine short patients (height < -1.8 SDS for chronological age) were divided into two groups (low and normal responders) on the basis of their GH peak during insulin and clonidine tests (< or = and > 20 mU/l, respectively). All but one low responders underwent the GHRH test to exclude the impairment of somatotroph function and in eight of them an IGF-1 generation test was also performed. The two groups were compared with each other with respect to growth (height deficiency, height velocity, bone age and bone delay), haematological characteristics (serum ferritin levels, age at the start both of low (subcutaneous) s.c. infusion of desferrioxamine and of transfusional therapy) and serum IGF-1 and IGF-1 binding protein 3 levels.

Thirteen patients (45%) (11 males, two females) were low responders, all but two having serum IGF-1 < 5th centile (< 0.1 centile in 42%); the GHRH test excluded the impairment of somatotroph function in 8/12. Height deficiency, serum ferritin levels, and age at the start of s.c. chelating therapy did not differ in low compared to normal responders. Height was negatively correlated both with the age at the start of s.c. chelating therapy and with serum ferritin levels.

The reduction of GH reserve, more frequently due to a hypothalamic than to a pituitary dysfunction, is frequent in polytransfused beta-thalassaemia patients, especially in males. The height function is not related to the GH reserve, given the current methods for testing GH reserve. Late start of s.c. chelating therapy as well as haemosiderosis seem to play a role in the height deficiency, but not in GH reserve. Impairment of GH secretory reserve, therefore, cannot be considered the main cause of height deficiency in these patients.