Age as a determinant of the impact of growth hormone therapy on predicted adult height.

OBJECTIVE

Final adult height is determined by both childhood and pubertal growth. The later is a function of growth velocity and bone maturation, and both are regulated by growth hormone. In a study of the safety and efficacy of GH therapy, we analysed the impact of age on bone maturation and predicted adult height.

PATIENTS AND METHODS

The subjects were 65 male patients with GH deficiency, as diagnosed by pharmacological or physiological tests, who participated in a multicentre trial and completed 3 years of hGH therapy. The age range at initiation of therapy was 3.1-15.7 years. Subcutaneous injections of hGH were given in a dose of 0.3 mg/kg/week, in thrice-weekly doses. Calculation of the adult height prediction was performed on annual growth parameters using the Bailey-Pinneau, TW-II and Roche methods.

RESULTS

The rate of pubertal advancement correlated positively with the child's age at initiation of therapy. The bone age advanced in positive correlation with chronological age, and by the end of 3 years of hGH therapy the delta-bone age/delta-chronological age ratio increased to 1.5 for children with an age at start of therapy of 10.7 years. During the adolescent years, the predicted gained height over 3 years of therapy declined, in correlation with age, and became negative at a therapy-initiation age of 12.9 years.

CONCLUSIONS

In a retrospective analysis of a group of children with heterogeneous GH secretory ability, GH induced acceleration of growth, around the age of normal puberty, advanced the age of pubertal onset and accelerated pubertal progression which, in turn, expedited bone maturation and thereby restricted predicted adult height gain from hGH therapy.