Indications for GH replacement in adolescents and young adults.

Data obtained from studies in childhood-onset GH deficiency (CO-GHD) in adult life indicate differences in body composition in comparison with adult-onset GHD, but the response to GH replacement is qualitatively similar in terms of reduction in fat mass, serum cholesterol and LDL-cholesterol. However, because bone development is GH dependent and achievement of peak bone mass occurs some years later than completion of linear growth, continuing somatic development is a potentially important issue in the GHD adolescent. This issue has been examined in a United Kingdom multicentre study, in which patients with persisting severe GHD were randomised to continue or discontinue GH replacement at completion of linear growth. Over the course of one years, important differences were observed in bone mineral content with continued accrual in patients continuing GH therapy, in comparison with minimal change in those patients who had discontinued. A similar pattern was observed for lean body mass. Both groups demonstrated gain in fat mass, with a tendency for this to be greater in the GH discontinuation group. There were no changes observed in lipoprotein profiles. These observations and similar data from other groups have provided the basis for recommendations that young adults with CO-GHD should be offered continuing GH replacement in order to optimise bone development. Despite the wide applicability of this advice, it should be recognised that there are significant interindividual differences in clinical characteristics. Further studies are required to determine whether sabbatical periods off GH replacement are clinically appropriate and, if so, their reasonable duration.