Novel approaches to short stature therapy

The Treatment of Growth Disorders in Childhood and Adolescence

BACKGROUND

3% of all children are unusually short, and 3% are unusually tall. New approaches have broadened the range of therapeutic options in treating growth disorders.

METHODS

This review is based on publications retrieved by a selective review of the literature and on the authors' clinical experience.

RESULTS

Pituitary growth hormone deficiency is treated with recombinant growth hormone. Long-acting preparations of this type became available recently, but their long-term safety and efficacy are still unknown. Vosoritide, a CNP analogue, has also been approved for the treatment of achondroplasia, and severe primary deficiency of insulin-like growth factor 1 (IGF-1) can be treated with recombinant IGF-1. In the treatment of excessively tall stature, new information on the safety of growth-attenuating treatment and an altered perception of above-average height in society have led to a change in management.

CONCLUSION

There are new options for the treatment of rare causes of short stature, while new information on the safety of treatment strategies for excessive tallness have led to a reconsideration of surgical intervention. There is insufficient evidence on the benefits and risks of supraphysiological GH therapy and of newer treatment options for which there are as yet no robust data on adult height. Therefore, before any treatment is provided, physicians should give patients and their families detailed information and discuss their expectations from treatment and the goals that treatment can be expected to achieve.

Use of letrozole to augment height outcome in pubertal boys: a retrospective chart review

OBJECTIVES

We describe growth patterns and predicted adult height (PAH) in pubertal boys treated with letrozole and evaluate the potential predictors of growth responses.

METHODS

We performed a retrospective analysis of data from 2002 to 2020. All subjects were treated for ≥6 months and had at least 3 height measurements to calculate the growth velocity (GV) before and during treatment. We evaluated growth measurements, bone age, and biochemical parameters before, during and after treatment.

RESULTS

A total of 59 subjects aged 12.7 (± 1.7) years old were included. At treatment initiation, bone age was 13.1 (± 1.5) years and predicted adult height (PAH) was 163.8 (± 9.9) cm compared to mid-parental height of 172.4 (± 5.8) cm. Growth velocity decreased during letrozole therapy and rebounded after completion. Sub-analysis of 26 subjects with bone age data available at baseline and at least 1 year later showed a trend to modest increase in PAH. In boys simultaneously receiving growth hormone (rhGH), the change in PAH was significantly more (3.2 cm, p<0.05) compared to those treated with letrozole alone.

CONCLUSIONS

We show that letrozole appropriately slows down skeletal maturation and GV responses are variable. Possible negative predictors include lower baseline GV and advanced bone age. A small positive trend in PAH with letrozole therapy is augmented by simultaneous use of rhGH. Future randomized controlled trials are needed to better understand which group of patients will benefit from treatment.

Progress on growth promoting therapies other than growth hormone

Recombinant human growth hormone is a classical therapeutic drug for children with short stature. In recent years, as the mechanism of growth in children has been further explored, growth-promoting therapies other than growth hormone have made great progress. Recombinant human insulin-like growth factor (IGF)-1 is the main treatment for primary IGF-1 deficiency, and C-type natriuretic peptide (CNP) offers a therapeutic option for children with short stature due to chondrodysplasia. Growth hormone-releasing peptide analogues stimulate growth hormone release and may be used for growth-promoting therapy. In addition, gonadotropin-releasing hormone analogue (GnRHa) and aromatase inhibitors may delay the bone age in children and may be beneficial in improving final height. In this article, the research progress of growth-promoting therapies other than growth hormones is reviewed to provide more options for the clinical treatment of children with short stature.

Diagnosis of Growth Hormone Deficiency Remains a Judgment Call - and That Is Good

The diagnosis of growth hormone deficiency (GHD) still does not reflect evidence-based and generally accepted practice, and reliance on growth hormone stimulation testing (GST) leads to a high rate of false-positive diagnosis of idiopathic-isolated GHD (IIGHD). While searching for more definitive indicators of GHD is attractive, it should not distract from currently available steps to reduce erroneous IIGHD diagnoses. This paper describes opportunities to improve the accuracy of the GST which include: (1) meticulous selection of candidates for GST, since a low prevalence of GHD among short children in general is a major factor undermining the test's diagnostic accuracy; (2) departure from traditional pass/fail diagnostic GH cutoffs toward, instead, formulation of diagnoses along a continuum that spans actual GHD - > provisional GHD - > not GHD; (3) response to the provisional diagnosis of IIGHD based on GST with additional post-test observation or alternative growth-promoting interventions rather than immediate human growth hormone treatment; (4) re-examination and often correction of a prior IIGHD diagnosis with the onset of puberty. Modern medicine is increasingly offering diagnostic tests that aim to eliminate the need for provisional diagnoses. But a pitfall of such a "definitive" test for GHD would be the temptation to respond to its results definitively. Given the nuances, variations, and fluctuations in GH axis function over time, children evaluated for growth concerns are still best served by clinical judgment that combines thoroughness, patience, flexibility, and healthy skepticism into the diagnosis of GHD.

Oxandrolone treatment in juvenile rats induced anxiety-like behavior in young adult animals

AIMS

Oxandrolone (OXA) is a synthetic steroid used for the treatment of clinical conditions associated with catabolic states in humans, including children. However, its behavioral effects are not well known. Our goal was to evaluate the anxiety-like behavior induced in young adult rats after the treatment of juvenile animals with OXA.

METHODS

Four-week-old male rats were separated into three groups: Control (CON), therapeutic-like OXA dose (TD), and excessive OXA dose (ED), in which 2.5 and 37.5 mg/kg/day of OXA were administered via gavage for four weeks for TD and ED, respectively. Behavior was evaluated through the elevated plus maze (EPM) and open field (OF) tests. Protein expression of catalase (CAT), superoxide dismutase (SOD), Tumor necrosis factor-α (TNF-α), and dopamine receptor 2 (DrD2) were analyzed in tissue samples of the hippocampus, amygdala, and prefrontal cortex by Western Blot.

RESULTS

OXA induced anxiety-like behaviors in both TD and ED animals; it decreased the time spent in the open arms of the EPM in both groups and reduced the time spent in the central zone of the OF in the TD group. In the hippocampus, CAT expression was higher in TD compared with both control and ED animals. No differences were found in the amygdala and prefrontal cortex. TNF-α, SOD, and DrD2 levels were not altered in any of the assessed areas.

CONCLUSIONS

Treatment of juvenile rats with OXA led to anxiety-like behavior in young adult animals regardless of the dose used, with minor changes in the antioxidant machinery located in the hippocampus.

Growth, growth potential, and influences on adult height in the transgender and gender-diverse population

The sexually dimorphic trait of height is one aspect of the experience of transgender and gender‐diverse (TGD) individuals that may influence their gender dysphoria and satisfaction with their transition. In this article, we have reviewed the current knowledge of the factors that contribute to one's final adult height and how it might be affected in TGD youth who have not experienced their gonadal puberty in the setting of receiving gonadotropin‐releasing hormone analog (GnRHa) and gender‐affirming hormonal treatment. Additional research is needed to characterize the influence of growth and final adult height on the lived experience of TGD youth and adults and how to best assess their growth, predict their final adult height, and how medical transition can be potentially modified to help them meet their goals.

Should Skeletal Maturation Be Manipulated for Extra Height Gain?

Skeletal maturation can be delayed by reducing the exposure to estrogens, either by halting pubertal development through administering a GnRH analogue (GnRHa), or by blocking the conversion of androgens to estrogens through an aromatase inhibitor (AI). These agents have been investigated in children with growth disorders (off-label), either alone or in combination with recombinant human growth hormone (rhGH). GnRHa is effective in attaining a normal adult height (AH) in the treatment of children with central precocious puberty, but its effect in short children with normal timing of puberty is equivocal. If rhGH-treated children with growth hormone deficiency or those who were born small-for-gestational age are still short at pubertal onset, co-treatment with a GnRHa for 2-3 years increases AH. A similar effect was seen by adding rhGH to GnRHa treatment of children with central precocious puberty with a poor AH prediction and by adding rhGH plus GnRHa to children with congenital adrenal hyperplasia with a poor predicted adult height on conventional treatment with gluco- and mineralocorticoids. In girls with idiopathic short stature and relatively early puberty, rhGH plus GnRHa increases AH. Administration of letrozole to boys with constitutional delay of growth puberty may increase AH, and rhGH plus anastrozole may increase AH in boys with growth hormone deficiency or idiopathic short stature, but the lack of data on attained AH and potential selective loss-of-follow-up in several studies precludes firm conclusions. GnRHas appear to have a good overall safety profile, while for aromatase inhibitors conflicting data have been reported.

The Actions of IGF-1 in the Growth Plate and Its Role in Postnatal Bone Elongation

PURPOSE OF REVIEW

Bone elongation is a complex process driven by multiple intrinsic (hormones, growth factors) and extrinsic (nutrition, environment) variables. Bones grow in length by endochondral ossification in cartilaginous growth plates at ends of developing long bones. This review provides an updated overview of the important factors that influence this process.

RECENT FINDINGS

Insulin-like growth factor-1 (IGF-1) is the major hormone required for growth and a drug for treating pediatric skeletal disorders. Temperature is an underrecognized environmental variable that also impacts linear growth. This paper reviews the current state of knowledge regarding the interaction of IGF-1 and environmental factors on bone elongation. Understanding how internal and external variables regulate bone lengthening is essential for developing and improving treatments for an array of bone elongation disorders. Future studies may benefit from understanding how these unique relationships could offer realistic new approaches for increasing bone length in different growth-limiting conditions.

The Challenge of Defining and Investigating the Causes of Idiopathic Short Stature and Finding an Effective Therapy

Idiopathic short stature (ISS) comprises a wide range of conditions associated with short stature that elude the conventional diagnostic work-up and are often caused by still largely unknown genetic variants. In the last decade, the improvement of diagnostic techniques has led to the discovery of causal mutations in genes involved in the function of the growth hormone (GH)/insulin-like growth factor-I (IGF-I) axis as well as in growth plate physiology. However, many cases of ISS remain idiopathic. In the future, the more frequent identification of the underlying causes will allow a better stratification of subjects and offer a tailored management. GH therapy has been proposed and approved in some countries for the treatment of children with ISS. To improve the efficacy of GH therapy, trials with GH combined with GnRH agonists, aromatase inhibitors, and even IGF-I have been conducted. This review aims to revise the current definition of ISS and discuss the management of children with ISS on the basis of the most recent evidence.

Abnormal linear growth in paediatric adrenal diseases: Pathogenesis, prevalence and management

Abnormal adrenal function can interfere with linear growth, potentially causing either acceleration or impairment of growth in paediatric patients. These abnormalities can be caused by direct effects of adrenal hormones, particularly glucocorticoids and sex steroids, or be mediated by indirect mechanisms such as the disturbance of the growth hormone-insulin-like growth factor-1 axis and aromatization of androgens to oestrogens. The early diagnosis and optimal treatment of adrenal disorders can prevent or minimize growth disturbance and facilitate improved height gain. Mechanisms of growth disturbance in the following abnormal states will be discussed; hypercortisolaemia, hyperandrogenaemia and obesity. Prevalence and features of growth disturbance will be discussed in ACTH-dependent and ACTH-independent Cushing's syndrome, adrenocortical tumours, premature adrenarche, congenital adrenal hyperplasia and adrenal insufficiency disorders. Recommendations for management have been included.

Achieving Optimal Short- and Long-term Responses to Paediatric Growth Hormone Therapy

It is over sixty years since the first administration of human growth hormone (GH) to children with GH deficiency, and over thirty years since recombinant human GH has been available for treatment of GH deficiency and a wider range of non-GH deficiency disorders. From a diagnostic perspective, genetic analysis, using single gene or Sanger sequencing and more recently next generation or whole exome sequencing, has brought advances in the diagnosis of specific causes of short stature, which has enabled therapy to be targeted more accurately. Genetic discoveries have ranged from defects of pituitary development and GH action to abnormalities in intracellular mechanisms, paracrine regulation and cartilage matrix formation. The strategy of GH therapy using standard doses has evolved to individualised GH dosing, depending on diagnosis and predictors of growth response. Evidence of efficacy of GH in GH deficiency, Turner syndrome and short children born small for gestational age is reviewed. The importance of critical assessment of growth response is discussed, together with the recognition and management of a poor or unsatisfactory growth response and the organisational issues related to prevention, detection and intervention regarding suboptimal adherence to GH therapy.

The Effect of Gonadotropin-Releasing Hormone Analogue on Final Adult Height in Children with Idiopathic Short Stature

OBJECTIVE

To assess final adult height (FAH) in children with short stature treated with gonadotropin-releasing hormone analogue (GnRHa).

METHODS

All patients with idiopathic short stature (ISS) with normally timed puberty and a Tanner stage between 2 and 3, who achieved their FAH between 2005 and 2015, were included in this clinical historical cohort study. Height gain, FAH, and mid-parental height of 28 children with ISS who received GnRHa treatment for 1.8 ± 1.0 years to delay their puberty were compared to 31 untreated children.

RESULTS

The FAHs of the treated and the untreated girls were 151.3 ± 5.1 and 146.8 ± 3.8 cm (p = 0.01), respectively. The FAHs of the treated and the untreated boys were 156.4 ± 4.7 and 152.3 ± 5.7 cm (p = 0.111), respectively. The height gain in the treated and the untreated girls was 1.6 ± 7.8 and -3.6 ± 5.7 cm (p = 0.036), respectively. Height gain in the treated and the untreated boys was -5.1 ± 13.6 and -11.5 ± 8.4 cm (p = 0.171), respectively.

CONCLUSION

GnRHa therapy has a modest effect in improving FAH in adolescent females with ISS but not in boys.

Genomic approaches to diagnose rare bone disorders

Skeletal dysplasias are Mendelian disorders with a prevalence of approximatively 1 in every 5000 individuals and can usually be diagnosed based on clinical and radiological findings. However, given that some diseases can be caused by several different genes, and that some genes can cause a variety of different phenotypes, achieving a molecular diagnosis can be challenging. We review here different approaches, from single gene sequencing to genomic approaches using next-generation sequencing, to reach a molecular diagnosis for skeletal dysplasias. We will further describe the overall advantages and limitations of first, second and third-generation sequencing, including single gene sequencing, whole-exome and genome sequencing (WES and WGS), multiple gene panel sequencing and single molecule sequencing. We also provide a brief overview of potential future applications of emerging technologies.

FIVE-YEAR OUTCOMES AFTER LONG-TERM OXANDROLONE ADMINISTRATION IN SEVERELY BURNED CHILDREN: A RANDOMIZED CLINICAL TRIAL

Administration of oxandrolone, a nonaromatizable testosterone analog, to children for 12 months following severe burn injury has been shown to improve height, increase bone mineral content (BMC), reduce cardiac work, and augment muscle strength. Surprisingly, the increase in BMC persists well beyond the period of oxandrolone administration. This study was undertaken to determine if administration of oxandrolone for 2 years yields greater effects on long-term BMC and bone mineral density (BMD). Patients between 0 and 18 years of age with ≥30% of total body surface area burned were consented to an IRB-approved protocol and randomized to receive either placebo (n = 84) or 0.1 mg/kg oxandrolone orally twice daily for 24 months (n = 35). Patients were followed prospectively from the time of admission until 5 years postburn in a single-center, intent-to-treat setting. Height, weight, BMC, and BMD were recorded annually through 5 years postinjury. The long-term administration of oxandrolone for 16 ± 1 months postburn (range, 12.1-25.2 months) significantly increased whole-body (WB) BMC (p < 0.02) and lumbar spine (LS) BMC (p < 0.05); these effects were significantly pronounced for a longer time in patients who were in growth spurt years (7-18 years). When adjusted for height, sex, and age, LS BMD was found to significantly increase with long-term oxandrolone administration (p < 0.0009). Fewer patients receiving oxandrolone exhibited LS BMD z scores below -2.0 as compared with controls, indicating a significantly reduced risk for future fracture with oxandrolone administration. Long-term oxandrolone patients had significantly greater height velocity than controls throughout the first 2-year postburn (p < 0.05). No adverse side effects were attributed to the long-term administration of oxandrolone. A comparison of the current patients receiving long-term oxandrolone to previously described patients receiving 12 months of oxandrolone revealed that long-term oxandrolone administration imparted significantly greater increases in WB-BMC, WB-BMD, and LS-BMD (p < 0.05). In conclusion, the administration of oxandrolone for up to 24 months to severely burned pediatric patients significantly improves WB BMC, LS BMC, LS BMD, and height velocity. The administration of long-term oxandrolone was more efficacious than administration for 12 months. Additionally, fewer patients in the oxandrolone cohort met the diagnostic criteria for pediatric osteoporosis, pointing to a reduced risk for future bone fracture. This study demonstrates that administering oxandrolone for up to 2 years following severe burn injury results in greater improvements in BMC, BMD, and height velocity.

Challenges in the Management of Short Stature

Human growth, from fetal life to adolescence, is dynamic and a good marker of health. Growth is a complex process influenced by genetic, hormonal, nutritional and environmental factors, both pre- and postnatally. To date, no international agreement regarding normal height has been established. Auxological parameters are fundamental to investigate potential short stature (SS), either with a known diagnosis, e.g. disproportionate or proportionate, prenatal and/or postnatal onset, or an unknown diagnosis, i.e. idiopathic SS. The incidence/prevalence of SS is difficult to establish. The measurement of choice in children aged <2 years is length, while in those >2 years of age it is height. A number of monogenic diseases that lead to proportionate SS due to either isolated growth hormone deficiency, multiple pituitary hormone deficiency, growth hormone insensitivity, primary acid-labile subunit deficiency, primary IGF-1 deficiency, IGF-1 resistance, primary IGF-2 deficiency or primary protease deficiency have been discovered in the last 30 years. In addition, the Nosology and Classification of Genetic Skeletal Disorders revised in 2015 includes 436 conditions, with a number of genes of 364. A practical algorithm for the evaluation of SS as well as therapeutic options are discussed.

Diagnosis and management of growth disorders in Gulf Cooperation Council (GCC) countries: Current procedures and key recommendations for best practice

Diagnosis and management of growth disorders comprises an important area of pediatric practice. Current procedures in the different stages of the identification, referral, investigation, and treatment of growth disorders in the Gulf Cooperation Council (GCC) countries have been summarized. Evidence-based procedures, relating specifically to height screening for identification of short stature, auxological criteria for patient referral from primary to secondary pediatric care, and general and endocrine investigations and diagnosis have been discussed and outlined. The management issues related to key disorders that are licensed for growth hormone (hGH) therapy, namely GH deficiency, Turner syndrome, short stature related to birth size small for gestational age (SGA), and idiopathic short stature are discussed with recommendations described for best practice. Finally, two key components of short stature management, namely transitional care for the transfer of patients from pediatric to adult endocrinology services and adherence to recommended therapy with hGH, have been addressed with current practice outlines and recommendations presented.

Genetic Techniques in the Evaluation of Short Stature

Normal growth is a complex dynamic process dependent on the coordination of multiple factors including genetics, nutrition and hormones that are all working in balance. This chapter will review selected features of commonly utilized genetic techniques such as chromosomal analysis, microarray analysis, targeted gene screening and whole exome sequencing that are being used to identify genes influencing growth. As genetic technologies continue to improve and become more accessible many of these techniques will help to provide a better understanding of mechanisms underlying abnormal growth and will eventually lead to novel management approaches for abnormal growth.

SHOX Haploinsufficiency as a Cause of Syndromic and Nonsyndromic Short Stature

SHOX in the short arm pseudoautosomal region (PAR1) of sex chromosomes is one of the major growth genes in humans. SHOX haploinsufficiency results in idiopathic short stature and Léri-Weill dyschondrosteosis and is associated with the short stature of patients with Turner syndrome. The SHOX protein likely controls chondrocyte apoptosis by regulating multiple target genes including BNP,Fgfr3, Agc1, and Ctgf. SHOX haploinsufficiency frequently results from deletions and duplications in PAR1 involving SHOX exons and/or the cis-acting enhancers, while exonic point mutations account for a small percentage of cases. The clinical severity of SHOX haploinsufficiency reflects hormonal conditions rather than mutation types. Growth hormone treatment seems to be beneficial for cases with SHOX haploinsufficiency, although the long-term outcomes of this therapy require confirmation. Future challenges in SHOX research include elucidating its precise function in the developing limbs, identifying additional cis-acting enhancers, and determining optimal therapeutic strategies for patients.