Efficacy and safety results of long-term growth hormone treatment of idiopathic short stature

Growth hormone and bone

PURPOSE OF REVIEW

Description of recent progress in our understanding of growth hormone (GH) effects on bone.

RECENT FINDINGS

Growth hormone deficiency is associated with low bone mass in children and adults, in addition to its well established impact on growth. Although GH and insulin-like growth factor I have direct skeletal actions, it is also possible that disordered parathyroid hormone secretion or effect may mediate some of the deleterious consequences of GH deficiency on bone. The benefits of GH replacement on bone mineral density have been demonstrated in many studies, but it remains unclear whether these are consistent across patient subgroups. The impact of GH replacement on fracture risk has not been definitively established. The positive effects of GH administration on growth are well established in childhood-onset growth hormone deficiency, as well as in several other pediatric conditions. Data on investigational uses of GH are also presented.

SUMMARY

GH may have a relevant role in bone physiology and several disease states in addition to growth hormone deficiency. Although the salutary effects of GH replacement on bone growth and bone density are well characterized, additional studies are required to examine the impact of GH replacement on fracture risk as well as potential benefits in osteoporosis.

Recombinant human insulin-like growth factor-1 treatment: ready for primetime

The combination of targeted gene knockout studies in animals and human mutational analysis has demonstrated the key role of the IGF system in mammalian growth, both in utero and postnatally. The concept of IGF deficiency as a diagnostic category for children with growth failure first was proposed in the mid 1990s, and has gained support through the demonstration of patients with mutations in key components of the growth hormone (GH)-IGF axis, as well as the widespread use of IGF-I assays for evaluating short stature. The US Food and Drug Administration has approved IGF-I therapy for treating children who have severe primary IGF deficiency, defined as a height SD score < or =-3 and a serum IGF-1 SD score < or =-3, normal serum GH. Recent studies have demonstrated the efficacy and safety of IGF-I therapy in such patients, and investigations are in progress to determine optimal dosing. The availability of IGF-I therapy thus has expanded the therapeutic tool chest available to endocrinologists caring for children who have growth failure.

[GH treatment in patients with idiopathic short stature]

Growth hormone has been used in the treatment of patients with idiopathic short stature. Clinical and laboratory criteria are discussed, taking into consideration the indication of GH and the evaluation of its efficacy and individual responsiveness. Anthropometric, psychosocial, ethical, and also cost/benefit aspects must be considered before GH prescription in idiopathic short stature patients.

Controversies in the definition and treatment of idiopathic short stature (ISS)

The term idiopathic short stature (ISS) refers to short children with no identifiable disorder of the growth hormone (GH)/insulin like growth factor (IGF) axis and no other endocrine, genetic or organ system disorder. This heterogeneous group of short children without GH deficiency (GHD) includes children with constitutional delay of growth and puberty, familial short stature, or both, as well as those with subtle cartilage and bone dysplasias. In rare cases, ISS is due to IGF molecular abnormalities. In this review we tackle the major challenges in the definition and treatment of ISS.

[Growth hormone and idiopathic short stature]

Idiopathic short stature is defined by height below 3rd percentile, in a child with normal birth height and weight, lack of dysmorphy, endocrine deficiency or systemic disease. Food and Drugs administration approved GH treatment in this indication in the United States, because it induces height gain, and sometimes may increase quality of life. There is no consensus in terms of duration, monitoring parameters, benefits and risks of long term GH treatment in these patients. Cost effectiveness of such a treatment is under debate, and ethical considerations also have to be taken into account. Recombinant IGF1 should not be proposed in this indication at the moment, due to the lack of sufficient data on potential GH insensitivity in a subgroup of these patients.

Acromegaly, growth hormone and cancer risk

Acromegaly is an endocrine disorder characterized by sustained hypersecretion of growth hormone (GH) with concomitant elevation of insulin-like growth factor I (IGF-I) associated with premature mortality from cardiopulmonary diseases and certain malignancies. In particular, there is a two-fold increased risk of developing colorectal cancer. Possible mechanisms underlying this association include elevated levels of circulating GH and IGF-I, but several other plausible processes may be relevant. In a parallel literature, there has been debate whether GH replacement therapy is associated with increased cancer risk in three scenarios: (1) tumour recurrence in children with previously treated cancer; (2) second neoplasms (SNs) in survivors of childhood cancer treated with GH; and (3) de-novo cancer in non-cancer patients treated with GH. The general evidence suggests no increased risk in scenario 1. Through a maze of complex study designs, there is inconclusive evidence of a very modest increase in cancer risk in treated GH-deficiency patients in scenarios 2 and 3, but it is likely that the cumulative risk equates to that of the general population. This emphasizes the need for patient selection balanced against the known morbidity of untreated GH deficiency.

Idiopathic short stature: management and growth hormone treatment

In the management of ISS auxological, biochemical, psychosocial and ethical elements have to be considered. In boys with constitutional delay of growth and puberty androgens are effective in increasing height and sexual characteristics, but adult height is unchanged. GH therapy is efficacious in increasing height velocity and adult height, but the inter-individual variation is considerable. The effect on psychosocial status is uncertain. Factors affecting final height gain include GH dose, height deficit in comparison to midparental height, age and first year height velocity. In case of a low predicted adult height at the onset of puberty, addition of a GnRH analogue can be considered. Although GH therapy appears safe, long-term monitoring is recommended.

Long-term safety of recombinant human growth hormone in turner syndrome

CONTEXT

Turner syndrome (TS) affects more than 50,000 girls and women in the United States. The National Cooperative Growth Study (NCGS) has collected efficacy and safety data for 5220 TS children treated with recombinant human GH (rhGH) during the last 20 yr.

OBJECTIVES

Our objective was to determine frequencies of specific targeted adverse events (AEs) and additional AEs of interest in TS patients. Corresponding safety data in non-TS patients or normal populations were compared for selected AEs.

METHODS

Patients may be enrolled at rhGH initiation and followed until discontinuation. Investigators submit AE reports describing any event that is potentially rhGH related or is a targeted event.

RESULTS

The Genentech Drug Safety department received 442 AE reports for TS NCGS patients as of June 30, 2006, including 117 serious AEs. Seven deaths occurred; five resulted from aortic dissections/ruptures. The incidence of certain events known to be associated with rhGH (targeted events), including intracranial hypertension, slipped capital femoral epiphysis, scoliosis, and pancreatitis, was increased compared with other non-TS patients in NCGS. There were 10 new-onset malignancies that occurred, including six in patients without known risk factors. Type 1 diabetes also appeared to be increased compared with other NCGS groups.

CONCLUSIONS

Children with TS who were treated with rhGH exhibit an increased underlying risk for selected AEs associated with rhGH and for type 1 diabetes, which is likely unrelated to rhGH. The aortic dissection/rupture incidence reflects the higher baseline risk for these events in TS, was consistent with current epidemiological data in smaller TS populations, and is likely unrelated to rhGH. It is not known whether the reported malignancies represent an inherently increased risk in TS patients. Twenty years of experience in 5220 patients indicates no new rhGH-related safety signals in the TS population. The NCGS and similar registries, although focused on the years during rhGH treatment, may also be a window into the natural history of TS in childhood.

Twenty years of recombinant human growth hormone in children: relevance to pediatric care providers

Recombinant human growth hormone has revolutionized the management of children and adolescents with growth hormone deficiency and other growth disorders, but clinical and ethical controversies remain regarding diagnostic approach, optimal recombinant human growth hormone dose and duration, and expected outcomes. Management of pubertal and transitioning patients with growth hormone deficiency has also commanded increased attention. Recent clinical studies that demonstrate the positive health benefits of recombinant human growth hormone in children with cystic fibrosis, inflammatory bowel disease, and juvenile rheumatoid arthritis have not yet clarified issues about patient selection and appropriate long-term use. An understanding of current recombinant human growth hormone indications and controversies can facilitate patient evaluation and expedite referral for potential treatment. This review summarizes current indications for recombinant human growth hormone use, discusses clinical challenges, and provides recommendations for pediatricians caring for children who may be appropriate candidates for recombinant human growth hormone therapy.

Growth hormone treatment of non-growth hormone-deficient growth disorders

Although a large body of data on efficacy and safety of growth hormone (GH) treatment for various non-growth hormone-deficient (GHD) growth disorders has accumulated from a combination of clinical trial and postmarketing sources in the last 20 years or more, there remain limitations. Clinical trial data have the advantage of direct comparison of well-matched, randomized patient groups receiving treatment (or not) under comparable conditions and, as such, provide the highest quality evidence of efficacy. Clinical trials, however, are typically too small for any statistically valid assessment for safety, which is more comprehensively addressed using postmarketing data. Consequently, while the efficacy of GH treatment in children with non-GHD growth disorders has been solidly established and, based on the combination of the rigor of the clinical trial data and numerical power of the postmarketing data, no major concerns exist regarding safety, additional long-term data are required.

Thymic hyperplasia in a child treated with growth hormone

OBJECTIVE

To report a case of thymic hyperplasia diagnosed three months after initiation of recombinant human growth hormone (GH) for the treatment of GH deficiency.

DESIGN

Retrospective chart review was conducted to evaluate the temporal relationship between treatment with GH and thymic enlargement in a 7-year-old girl who had a history of embryonal rhabdomyosarcoma of the nasopharynx diagnosed at the age of 3 years.

RESULTS

The diagnosis of GH deficiency was made based on clinical and auxological criteria, an insufficient response to clonidine-arginine stimulation testing (peak GH level of 4.8 microg/L) and low insulin-like growth factor 1 (IGF-1) level (30 ng/mL, -2.7 SD). The patient was started on GH at a dose of 0.3mg/kg/week. At the initiation of treatment with GH, the baseline growth velocity was 0.8 cm/year (-6.0 SD) and height was 112.5 cm (-1.7 SD). After three months of treatment with GH, her height increased by 4.2 cm (from -1.7 to -1.2 SD), and the IGF-1 level from -2.7 SD to -1.1 SD. A chest CT performed at that time for recurrence surveillance showed 89% increase in thymic volume relative to previous scan before treatment with growth hormone. A thoracoscopic biopsy of the thymus was performed and revealed hyperplasia with normal thymic architecture without evidence of malignancy.

CONCLUSIONS

The timing of the development of thymic hyperplasia, along with data from in vitro and in vivo animal studies showing that GH and IGF-1 can directly stimulate growth of the thymus, suggests that GH contributed to the development of thymic hyperplasia in this patient.

Growth hormone is effective in treatment of short stature associated with short stature homeobox-containing gene deficiency: Two-year results of a randomized, controlled, multicenter trial

BACKGROUND

The short stature homeobox-containing gene, SHOX, located on the distal ends of the X and Y chromosomes, encodes a homeodomain transcription factor responsible for a significant proportion of long-bone growth. Patients with mutations or deletions of SHOX, including those with Turner syndrome (TS) who are haplo-insufficient for SHOX, have variable degrees of growth impairment, with or without a spectrum of skeletal anomalies consistent with dyschondrosteosis.

OBJECTIVE

Our objective was to determine the efficacy of GH in treating short stature associated with short stature homeobox-containing gene deficiency (SHOX-D).

DESIGN AND METHODS

Fifty-two prepubertal subjects (24 male, 28 female; age, 3.0-12.3 yr) with a molecularly proven SHOX gene defect and height below the third percentile for age and gender (or height below the 10th percentile and height velocity below the 25th percentile) were randomized to either a GH-treatment group (n = 27) or an untreated control group (n = 25) for 2 yr. To compare the GH treatment effect between subjects with SHOX-D and those with TS, a third study group, 26 patients with TS aged 4.5-11.8 yr, also received GH. Between-group comparisons of first-year and second-year height velocity, height sd score, and height gain (cm) were performed using analysis of covariance accounting for diagnosis, sex, and baseline age.

RESULTS

The GH-treated SHOX-D group had a significantly greater first-year height velocity than the untreated control group (mean +/- se, 8.7 +/- 0.3 vs. 5.2 +/- 0.2 cm/yr; P < 0.001) and similar first-year height velocity to GH-treated subjects with TS (8.9 +/- 0.4 cm/yr; P = 0.592). GH-treated subjects also had significantly greater second-year height velocity (7.3 +/- 0.2 vs. 5.4 +/- 0.2 cm/yr; P < 0.001), second-year height sd score (-2.1 +/- 0.2 vs.-3.0 +/- 0.2; P < 0.001) and second-year height gain (16.4 +/- 0.4 vs. 10.5 +/- 0.4 cm; P < 0.001) than untreated subjects.

CONCLUSIONS

This large-scale, randomized, multicenter clinical trial in subjects with SHOX-D demonstrates marked, highly significant, GH-stimulated increases in height velocity and height SDS during the 2-yr study period. The efficacy of GH treatment in subjects with SHOX-D was equivalent to that seen in subjects with TS. We conclude that GH is effective in improving the linear growth of patients with various forms of SHOX-D.

Individualized therapy for growth hormone deficiency

The use of human growth hormone to treat children with short stature resulting from growth hormone deficiency or insufficiency has now accrued over 40 years of clinical experience with a satisfactory safety and efficacy record. Growth hormone deficiency is the primary indication for growth hormone treatment in childhood. It is basically a clinical diagnosis, based upon auxologic features, and confirmed by biochemical testing. For assurance of compliance, dosing and, perhaps, safety considerations, a dosing algorithm based upon insulin-like growth factor-I response seems to be appropriate. Current data suggest that such algorithms reflect the true growth hormone needs of a patient, and allow optimization of growth hormone treatment. For patients who display a suboptimal growth response or in whom the insulin growth factor levels remain low with assurance of adherence to the injection schedule, it is reasonable to increase the growth hormone dose. The availability of recombinant human insulin-like growth factor-I treatment may provide an alternative for massively increasing the dose of growth hormone. Dose reductions should be considered for patients with serum insulin-like growth factor-I levels substantially above the normal range.