Dr. Vinutha B Shetty , Endocrinology Fellow
Princess Margaret Hospital For Children
Growth hormone (GH) is a hormone released from a gland in the brain known as the pituitary gland. It is well-known that growth hormone (GH) stimulates growth in children. However research in the last few decades has shown that GH also plays a critical role in metabolism and in the maintenance of physical fitness and health in adults.
GH is the most abundant hormone in the pituitary gland and continues to be produced throughout adult life. The effects of GH are widespread and it plays a general role in maintaining the metabolic process and the integrity of many tissues in the body in the adult which include: promotion of linear growth, maintenance of normal body composition (bone and muscle) and metabolism through adult life.
Growth hormone has been used to treat children with growth problems for many years. As with any treatment there are potential side effects, but fortunately significant side effects of growth hormone treatment are rare.
The specific aims of GH therapy for children are as follows:
1. To promote short-term catch-up growth in children of short stature.
2. To enhance long-term linear growth in children of short stature.
3. To allow children to achieve their familial genetic adult height potential, and where possible to achieve a final
within the normal population range.
4. To correct neonatal hypoglycaemia due to GH deficiency.
5. To ensure GH therapy is safe and
6. To improve linear growth and body composition for patients with Prader-Willi Syndrome.
Transition period is the period from late puberty till full adult maturation, with completion of bone and muscle development. This usually implies a period from mid to late teens until 6–7 years after achievement of final height. It is an important phase of growth, in particular, the development of bone mass is critical during this period. It is now recognized that the continuation of GH therapy in the transition years is required to achieve adult levels of bone and muscle development. Hence “transitional years” is an appropriate time to provide some guidance on the assessment of those completing treatment with GH.
Growth Hormone (GH) is subsidised by the Australian Government through the Pharmaceutical Benefits Scheme (PBS). The PBS GH Program is primarily concerned with the growth-promoting effects of GH, namely enhancement of linear growth. Subsidised treatment continues until skeletal maturity is reached. Most children on the scheme will be deemed “adults” under the current criteria at the age of 14 years. With the current evidence, ceasing GH therapy soon after final height, the age when normal subjects are still increasing bone mass, has significant implications in patients with severe Growth Hormone Deficiency (GHD). It limits development of bone and muscle mass, increases fat accumulation around the abdomen and decreases muscle strength.
The GH replacement strategy differs in childhood from that adopted in adult life. In childhood all degrees of GHD are considered for replacement. In adult life only patients with severe GHD are currently treated. Hence there is a need for re-evaluation of the diagnosis when the major paediatric goals of treatment have been reached. All patients require re-evaluation of pituitary function during transition, with the only exception being those with severe pituitary hormone deficiencies, (4 or 5 hormone deficiencies), where GH can be continued without interruption. Thus, in adolescents with GHD, treatment should be stopped for re-evaluation of the diagnosis when growth and pubertal development are considered to be complete.
In older adolescents and young adults with severe GHD, there is now evidence that show, the negative consequences of interrupting GH replacement and the positive effects of continued treatment on body composition, exercise capacity, bone strength and quality of life.
Endocrine Society Clinical Practice Guidelines on treatment of adult GH deficiency was recently updated and they recommend after documentation of persistent Growth Hormone Deficiency, that GH therapy be continued after completion of adult height to obtain full skeletal/muscle maturation during the transition period. In the transition phase, GH dose is much lower compared to the doses required during childhood for growth promotion.
The government funding for growth hormone replacement for children with growth hormone deficiency ceases once the final height is reached. The Endocrine Society of Australia (ESA) and Australasian Paediatric Endocrine Group (APEG) are putting in a submission to PBAC for approval of continuation of GH treatment till 25 years of age. We hope that it is approved, which would result in availability of subsidised GH therapy to appropriate candidates with GH deficiency through the transitional years.