Growth hormone deficiency throughout puberty

Sex steroid priming in short stature children unresponsive to GH stimulation tests: Why, who, when and how

Despite decades of experience, the diagnosis of growth hormone deficiency (GHD) remains challenging, especially in peripubertal children. Failure to respond to GH stimulation tests (GHSTs) is needed to confirm GHD, but long-standing controversies regarding the number of tests needed and the interpretation of GH peaks are still a matter of debate worldwide. Diagnostic workup is even more problematic in short children with slow growth and delayed sexual development: they often exhibit low GH peaks under GHST, which often normalize as puberty progresses. Consequently, this transient suboptimal response to GHST may result in GH overtreatment, carrying both health and economic concerns. Considering the complex and bound link between GH axis and sex steroids, the use of sex steroid priming prior to GHST might be helpful in peripubertal setting. However, its use is still controversial. There is no consensus regarding patient selection, timing, dose, and preparation of sex steroids. In this review, we aim to overview the use of sex steroid priming in clinical practice, highlighting the need to develop appropriate guidelines in order to overcome diagnostic pitfalls in peripubertal age.

The impact of the GH-IGF-I axis on gonadotropin secretion: inferences from animal models

Given the tight, temporal coupling between growth and reproductive development, the idea that a common signal may regulate both adolescent growth and the initiation of puberty has been the focus of much research. Since the rate-limiting step for the onset of puberty is the appropriate hypothalamic secretion of gonadotropin-releasing hormone (GnRH), any factor important for the initiation of puberty must affect GnRH pulsatility. This review examines the hypothesis that GH and/or IGF-I are growth-related signals that regulate the release of GnRH, initiating puberty. By extension, this review also addresses the hypothesis that the GH axis also impacts GnRH and gonadotropin secretion in post-pubertal individuals and, thus, affects the maintenance of fertility in adults. The review examines data from a range of animal models employing a number of different strategies which directly manipulate the activity of either GH or IGF-I. The success of these strategies for producing the desired effects on the GH-IGF-I axis is somewhat variable. Although IGF-I may only play a permissive role in the maintenance of adult fertility, acting at the level of the gonad to increase sensitivity to gonadotropin stimulation, the data indicate that IGF-I is essential for reproductive maturation. However, in addition to its well-documented effects on the gonad, the specific mode of action of IGF-I on the neuroendocrine hypothalamus and GnRH pulsatility remains to be determined. Available evidence suggests that such action by IGF-I may be mediated through neurotransmitter effects on GnRH neurons, changing the availability of metabolic substrates for neuronal activity, or remodeling of synaptic input into GnRH neurons.

Unfavorable effects of growth hormone therapy on the final height of boys with short stature not caused by growth hormone deficiency

A group of 18 boys with non-growth hormone (GH)-deficient short stature without GH therapy (group A) and another group of 9 boys with non-GH-deficient short stature with GH therapy in doses of 0.5 IU (0.17 mg)/kg per week administered 5 to 6 times weekly (group B) were observed until they reached their final height. The mean duration of GH therapy was 4.2 years (range 3.2 to 5.0 years). These two groups were matched with respect to their standard deviation score (SDS) for bone age at the start of observation. Mean +/- SD of the final height for group A and group B was 162.0 +/- 5.4 cm and 154.2 +/- 4.2 cm, respectively. During the prepubertal period, height SDS for bone age of these two groups was not affected by GH therapy. During the pubertal period, however, height SDS for bone age remained constant for group A but decreased gradually for group B. Our observation indicates that for boys with non-GH-deficient short stature GH therapy does not improve height SDS for bone age during the prepubertal period, and in fact reduces it during the pubertal period, possibly resulting in a shorter final height than might have been attained naturally.