Growth hormone neurosecretory dysfunction

GHRH-GH-IGF1 axis in pediatric Down syndrome: A systematic review and mini meta-analysis

Objective

To analyze and determine the quality of functioning in different components of GHRH-GH-IGF1 axis in children with Down syndrome (DS).

Design

Systematic review and mini meta-analysis of the literature.

Methods

A search was performed in PubMed, Embase, Scopus, and PsycINFO through August 2022. Eligible studies included pediatric patients with DS who had undergone any laboratory evaluation of the GHRH-GH-IGF1 axis. Two reviewers independently screened articles for eligibility. Results of each type of test were weighed together in patients both with and without DS and were pooled using a random effects meta-analysis.

Results

In total, 20 studies assessed the GHRH-GH-IGF1 axis function. A defect in three major components of GHRH-GH-IGF1 axis was found in a significant proportion of pediatric DS patients.

Conclusions

A significant portion of short-stature pathogenesis in children with DS is associated with impaired GHRH-GH-IGF1 axis function.

A Proposal for the Interpretation of Serum IGF-I Concentration as Part of Laboratory Screening in Children with Growth Failure

The serum insulin-like growth factor-I (IGF-I) concentration is commonly used as a screening tool for growth hormone deficiency (GHD), but there is no consensus on the cut-off limit of IGF-I standard deviation score (SDS) to perform GH stimulation tests for confirmation or exclusion of GHD. We argue that the cut-off limit is dependent on the clinical pre-test likelihood of GHD and propose a diagnostic strategy in which the cut-off limit varies between zero to -2 SDS.

Recombinant Human Growth Hormone (rhGH) Treatment of Children Undergoing Peritoneal Dialysis

The authors studied the effect of recombinant growth hormone (rhGH) treatment on 5 growth retarded children, age 21/12 to 178/12 years, who had end-stage renal disease (ESRD) and were undergoing continuous cycling peritoneal dialysis (CCPD). Patients received 0.125 mg/kg of subcutaneous rhGH 3 times weekly. Accelerated height velocity compared to the previous year of CCPD was noted in 2 patients and improvement in the standard deviation score (SDS) as a parameter of improved growth velocity was noted in a third patient. This was associated with an increase in weight and improvement in the midarm muscle circumference (MAMC) suggesting an anabolic effect of rhGH treatment. Bone age advancement was consistent with the period of observation; no advancement greater than that expected for the increase in chronological age was observed. No significant side effects were attributable to rhGH therapy. These preliminary results indicate some growth retarded children without growth hormone deficiency with ESRD undergoing CCPD may respond to exogenous rhGH therapy with an acceleration in growth velocity: However, the failure to achieve uniform acceleration of height velocity indicates the need for controlled studies before rhGH can be recommended for all growth retarded children with ESRD undergoing peritoneal dialysis.

Pituitary volume in children with growth hormone deficiency, idiopathic short stature and controls

BACKGROUND

The objective of the study was to describe the pituitary volume (PV) in pediatric patients with isolated growth hormone deficiency (IGHD), idiopathic short stature (ISS) and normal controls.

METHODS

Sixty-nine patients (57 male, 12 female), with a mean age of 11.9 (±2.0), were determined to have IGHD. ISS was identified in 29 patients (20 male, 9 female), with a mean age of 12.7 (±3.7). Sixty-six controls (28 female, 38 male), mean age 9.8 (±4.7) were also included. Three-dimensional (3D) magnetic resonance images with contrast were obtained to accurately measure PV.

RESULTS

There was a significant difference in the mean PV among the three groups. The IGHD patients had a mean PV 230.8 (±89.6), for ISS patients it was 286.8 (±108.2) and for controls it was 343.7 (±145.9) (p<0.001). There was a normal increase in PV with age in the ISS patients and controls, but a minimal increase in the IGHD patients.

CONCLUSIONS

Those patients with isolated GHD have the greatest reduction in PV compared to controls and the patients with ISS fall in between. We speculate that a possible cause for the slowed growth in some ISS patients might be related to diminished chronic secretion of growth hormone over time, albeit having adequate pituitary reserves to respond acutely to GH stimulation. Thus, what was called neurosecretory GHD in the past, might, in some patients, be relative pituitary hypoplasia and resultant diminished growth hormone secretion. Thus, PV determinations by magnetic resonance imaging (MRI) could assist in the diagnostic evaluation of the slowly growing child.

Radiotherapy-induced hypopituitarism: a review

Hypopituitarism is a disorder caused by impaired hormonal secretions from the hypothalamic-pituitary axis. Radiotherapy is the most common cause of iatrogenic hypopituitarism. The hypothalamic-pituitary axis inadvertently gets irradiated in patients receiving prophylactic cranial radiotherapy for leukemia, total body irradiation and radiotherapy for intracranial, base skull, sinonasal and nasopharyngeal tumors. Radiation-induced hypopituitarism (RIH) is insidious, progressive and largely nonreversible. Mostly, RIH involves one hypothalamic-pituitary axis; however, multiple hormonal axes deficiency starts developing at higher doses. Although the clinical effects of the hypopituitarism are more profound in children and young adults, its implications in older adults are being increasingly recognized. The risk continues to persist or increase up to 10 years following radiation exposure. The clinical management of hypopituitarism is challenging both for the patients and healthcare providers. Here we have reviewed the scale of the problem, the risk factors and the management of RIH.

Height as a potential indicator of early life events predicting Parkinson's disease: A case-control study

Aim of this study was to investigate the relationship between height in young adult age and Parkinson's disease (PD) risk. We included 266 persons affected by idiopathic PD. Patients were matched by age and sex to 266 controls by a random selection from the municipality of residence. We collected information about height preceding PD from official documents where these characteristics referred to young adult age (nearly 30 years). We compared height in cases and controls by calculating differences in mean distribution and by chi(2) analyses. Crude and adjusted odds ratios (OR) and 95% confidence intervals (CI) were calculated by logistic regression models. Mean height was significantly lower in persons affected by PD compared to controls (P = 0.03). Difference was significant only in men (P = 0.001). Logistic regression models showed an inverse association between height and PD (OR 0.35; CI 0.16, 0.79; P < 0.01 comparing individuals in the highest percentiles of height with those in the lowest). Our results indicate an association between height and PD in men. Considering that dopamine sensitivity in the hypothalamic-pituitary axis is related to adult height, our findings suggest a relationship between PD and factors modulating somatic growth early in life.

Cranial irradiation and growth hormone neurosecretory dysfunction: a critical appraisal

CONTEXT

It has been suggested that radiation-induced GH neurosecretory dysfunction exists in children; however, the pathophysiology is poorly understood, and it is unknown if such a phenomenon exists in adult life.

STUDY SUBJECTS

Twenty-four-hour spontaneous GH secretion was studied by 20-min sampling both in the fed state (n = 16; six women) and the last 24 h of 33-h fast (n = 10; three women) in adult cancer survivors of normal GH status defined by two GH provocative tests, 13.1 +/- 1.6 (range, 3-28) yr after cranial irradiation (18-40 Gy) for nonpituitary brain tumors (n = 12) or leukemia (n = 4) in comparison with 30 (nine women) age- and body mass index-matched normal controls (fasting, 11 men and three women).

RESULTS

Using previously published diagnostic thresholds, all patients had stimulated peak GH responses in the normal range to both the insulin tolerance test and the combined GHRH plus arginine stimulation test, as well as normal individual mean profile GH levels during the fed and fasting states. However, gender-specific comparisons revealed marked reduction (by 40%) in the overall peak GH responses to both provocative tests but similar GH secretory profiles; no differences were seen in the pulsatile attributes of GH secretion (cluster analysis) or the profile absolute and mean GH levels in the fed state or when the hypothalamic-pituitary axis was stimulated by fasting.

CONCLUSIONS

Radiation-induced GH neurosecretory dysfunction either does not exist or is a very rare phenomenon in irradiated adult cancer survivors. The normality of physiological GH secretion in the context of reduced maximum somatotroph reserve suggests compensatory overdrive of the partially damaged somatotroph axis and constitutes a relative argument against somatotroph dysfunction being explained purely by hypothalamic damage with secondary atrophy due to GHRH deficiency. It is therefore possible that radiation in doses less than 40 Gy causes dual damage to both the pituitary and the hypothalamus.

Pathophysiology of radiation-induced growth hormone deficiency: efficacy and safety of GH replacement

Radiation-induced growth hormone deficiency (GHD) is primarily due to hypothalamic damage. GH secretion by the pituitary may be affected either secondary to some degree of quantitative deprivation of hypothalamic input or, if the radiation dose is high enough, by direct pituitary damage. As a consequence, the neurosecretory profile of GH secretion in an irradiated patient remains pulsatile and qualitatively intact. The frequency of pulse generation is unaffected, but the amplitude of the GH pulses is markedly reduced. Over the last 25 years, the final heights achieved by children receiving GH replacement for radiation-induced GHD have improved; these improvements are attributable to refinements in GH dosing schedules, increased use of GnRH analogues for radiation-induced precocious puberty, and a reduced time interval between completion of irradiation and initiation of GH therapy. When retested at the completion of growth, 80-90% of these teenagers are likely to prove severely GH deficient and, therefore, will potentially benefit from GH replacement in adult life. Such long-term GH treatment in patients treated previously for a brain tumor means that critical and continuous surveillance must be devoted to the risk of tumor recurrence and the possibility of second neoplasms.

Hypopituitarism as a consequence of brain tumours and radiotherapy

Radiation-induced damage to the hypothalamic-pituitary (h-p) axis is associated with a wide spectrum of subtle and frank abnormalities in anterior pituitary hormones secretion. The frequency, rapidity of onset and the severity of these abnormalities correlate with the total radiation dose delivered to the h-p axis, as well as the fraction size, younger age at irradiation, prior pituitary compromise by tumour and/or surgery and the length of follow up. Whilst, the hypothalamus is the primary site of radiation-induced damage, secondary pituitary atrophy evolves with time due to impaired secretion of hypothalamic trophic factors and/or time-dependent direct radiation-induced damage. Selective radiosensitivity in the neuroendocrine axes with the GH axis being the most vulnerable to radiation damage accounts for the high frequency of GH deficiency, which usually occurs in isolation following irradiation of the h-p axis with doses less than 30 Gy. With higher radiation doses (30-50 Gy), however, the frequency of GH insufficiency substantially increases and can be as high as 50-100%, and TSH and ACTH deficiency start to occur with a long-term cumulative frequency of 3-6%. Abnormalities in gonadotrophin secretion are dose-dependent; precocious puberty can occur after radiation dose less than 30 Gy in girls only, and in both sexes equally with a radiation dose of 30-50 Gy. Gonadotrophin deficiency occurs infrequently and is usually a long-term complication following a minimum radiation dose of 30 Gy. Hyperprolactinemia, due to hypothalamic damage leading to reduced dopamine release, has been described in both sexes and all ages but is mostly seen in young women after intensive irradiation and is usually subclinical. A much higher incidence of gonadotrophin, ACTH and TSH deficiencies (30-60% after 10 years) occur after more intensive irradiation (>70 Gy) used for nasopharyngeal carcinomas and tumours of the skull base and following conventional irradiation (30-50 Gy) for pituitary tumours. Radiation-induced anterior pituitary hormone deficiencies are irreversible and progressive. Regular testing is mandatory to ensure timely diagnosis and early hormone replacement therapy to improve linear growth and prevent short stature in children cured from cancer, and in adults preserve sexual function, prevent ill health and osteoporosis and improve the quality of life.

Disturbances of growth and endocrine function after busulphan-based conditioning for haematopoietic stem cell transplantation during infancy and childhood

It is generally assumed that busulphan/cyclophoshamide (Bu/Cy)-based conditioning regimens for haematopoietic stem cell transplantation (SCT) do not affect growth. We evaluated growth and endocrine function after Bu/Cy-based conditioning in 64 children without a history of irradiation. Mean height standard deviation scores remained stable, but unexplained disturbances of growth after SCT were found in 17/48 (35%) of the children without growth-limiting disorders (10/23 in patients treated for haematological malignancies). In 10 patients, growth hormone (GH) secretion status was evaluated, and insufficient GH secretion was diagnosed in four patients. Thyroid function was evaluable in 52 patients. Two developed antibody-mediated thyroid disorders and 10 (19%) compensated primary hypothyroidism. Gonadal function was evaluable in 21 patients and was normal in all seven patients treated with low-dose Bu (8 mg/kg), whereas seven of the 14 children receiving high-dose Bu (16-20 mg/kg) developed gonadal failure; the majority of these patients had not been exposed to gonadotoxic therapy prior to Bu/Cy. Of the 49 evaluable patients, 16 developed subclinical hyperparathyroidism. We conclude that, besides gonadal and thyroid dysfunction, impaired growth and hyperparathyroidism often occur after Bu/Cy conditioning for SCT and that growth impairment may be the result of insufficient GH secretion.

Growth hormone therapy in elderly people: an age-delaying drug?

The aims of this review are to present a brief overview of growth hormone (GH) physiology and to summarize the studies of GH treatment in adults. Special attention has been paid to randomized controlled trials. Studies have revealed a partial deficiency of GH secretion in the elderly. GH secretion on the average declines by 14% with each decade in normal adults after 20 years of age. Aging has a central effect on the GH secretion and peripheric effect on insulin-like growth factor 1 (IGF-1) through changes in the body composition. GH administration may attenuate several important decrements in body composition and in function associated with aging. GH may also have very potent anabolic effects in surgical situations. Short-term side-effects of GH therapy include edema, carpal tunnel syndrome and arthralgia. A number of agents such as oral GH-releasing peptides (GHRPs) increase GH secretion; they may be an alternative to GH treatment in the future. Further studies of GH replacement are needed, examining issues such as dosage, tolerance and efficacy before the widespread use of GH in the elderly is advocated.

Neuroendocrine studies in dementia patients: responses of plasma GH and PRL following bromocriptine administration

Bromocriptine stimulates growth hormone (GH) secretion at the hypothalamus and suppresses prolactin (PRL) secretion at the pituitary level. We administered bromocriptine to 30 patients with dementia of the Alzheimer type (DAT), 30 patients with multi-infarct dementia (MID) and 22 age matched healthy controls, and compared response patterns of GH and PRL. Incomplete PRL suppressive responses (suppression rate < 50%) were seen in 36.7% of DAT patients and in 30.0% of MID patients, indicating that both groups had the same degree of pituitary dysfunctions. Blunted GH responses (< 5 ng/ml) were seen in 93.3% of DAT patients, in 63.3% of MID patients and in 31.8% of the controls. The results indicate that neuroendocrine regulation of GH is more selectively and severely damaged in DAT patients than in MID patients at the hypothalamus.

Effect of two consecutive administrations of GHRH in children with constitutional growth delay

It has been suggested that children with constitutional growth delay might have a transient immaturity of the neurotransmitter pathways necessary for the control of growth hormone releasing hormone (GHRH) secretion. In this study we evaluated the effects of two consecutive GHRH boluses (1 microgram/kg, i.v.) in nine prepubertal boys with constitutional growth delay. Growth hormone (GH) responses to GHRH administration were similar to that observed in normal children (first GHRH bolus, GH net incremental area under the curve (nAUC) +/- SE: 788 +/- 244 vs 984 +/- 242 ng/ml per hour; second bolus, GHnAUC: 657 +/- 122 vs 541 +/- 129 ng/ml per hour, respectively). These data suggest that no relevant abnormalities in the mechanisms determining the somatotroph sensitivity to GHRH are present in children with constitutional growth delay.

Attenuation of spontaneous, nocturnal growth hormone secretion in children with hypothyroidism and its correlation with plasma insulin-like growth factor I concentrations

To define further the alterations in growth hormone (GH) secretion that occur in childhood hypothyroidism, we quantified spontaneous nocturnal secretion in seven patients with primary hypothyroidism. We examined the relationship between plasma insulin-like growth factor I (IGF-I) and GH secretory profile in each patient before and during therapy with L-thyroxine. In contrast to the results of previous studies that used pharmacologic tests of GH release, spontaneous GH secretion was consistently attenuated in the hypothyroid state. Mean nocturnal GH levels were reduced by 58% (1.48 +/- 0.38 ng/ml, mean +/- SEM) in comparison with values obtained during L-thyroxine therapy (3.54 +/- 0.71 ng/ml, p less than 0.01). Coincident with the reduced levels of GH, plasma IGF-I concentrations were lower in patients before therapy (0.46 +/- 0.20 U/ml) compared with concentrations during therapy (1.50 +/- 0.34 U/ml, p less than 0.01). In treated, euthyroid patients, GH and IGF-I levels were equivalent to those of normal children. The excellent correlation (r = 0.77) between plasma IGF-I and mean nocturnal GH concentrations indicates that reduced plasma IGF-I levels in hypothyroidism probably result from suppressed GH secretion.

Human growth hormone in urine: development of an ultrasensitive radiometric assay

An immunoradiometric assay for human growth hormone (HGH) has been developed which has a detection limit of 1 ng/l and can measure HGH in unextracted urine from normal children and adults. The assay is based on a two-step procedure, using a solid-phase goat-anti-HGH immunosorbent for immunoextraction and [125I]-labeled monoclonal HGH-antibody for detection and quantification. The assay is not affected by urea, NaCl or changes of pH from 5-8. The mean urine HGH concentration in normal children is 6.78 +/- 7.6 (SD) pg/ml, in patients with HGH-deficiency 1.3 +/- 0.9 pg/ml which increases to 11.7 +/- 13.4 pg/ml on the day of growth hormone injection.

The molecular basis of growth hormone deficiency

A well-known law states that 'if a thing can go wrong it will go wrong'. This clearly applies to the hypothalamic-pituitary-somatic axis as to many other physiological and biochemical systems. Defects of this axis, giving rise to stunted growth, can occur at several different points, as has been discussed in detail in this review. Defects at the level of the brain can lead to inadequate production or secretion of the factors that control growth hormone secretion. Defects at the level of the pituitary can lead to failure to produce or secrete adequate quantities of growth hormone, or to production of inactive hormone. Defects at the level of target organs can lead to inability to respond to growth hormone or somatomedins. The axis involved in the production and effects of growth hormone is a complex one, and defects have been identified at most of the points that 'could go wrong', although in many cases the molecular details are far from fully understood. Increased understanding of the biochemistry and physiology of the hormonal control of growth, and of the impairments to which it is subject, should provide an improved basis for treatment of growth defects. Nevertheless, there remain many points at which our knowledge is very incomplete. The field is a rapidly moving one and further developments in both basic understanding and clinical treatment are to be expected during the next few years.