Growth hormone deficiency pathophysiology
|
Growth hormone deficiency Microchapters |
|
Differentiating Growth hormone deficiency from other Diseases |
|---|
|
Diagnosis |
|
Treatment |
|
Case Studies |
|
Growth hormone deficiency pathophysiology On the Web |
|
American Roentgen Ray Society Images of Growth hormone deficiency pathophysiology |
|
Risk calculators and risk factors for Growth hormone deficiency pathophysiology |
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief:
Overview
Pathophysiology
- The somatotroph cells of the anterior pituitary gland produce growth hormone.
- They are regulated by two hypothalamic hormones; GH-releasing hormone (GHRH) stimulates and somatostatin inhibits them.
GH best-known effect is increasing body mass.
- GH increases total body protein content, decreases total body fat content, and increases fat deposition in the liver.
- The effects on fat are due to stimulation of lipolysis and reciprocal antagonism of the lipogenic action of insulin in peripheral fat stores.
- GH also increases bone mass by stimulating skeletal insulin-like growth factor-I (IGF-I) synthesis and causing proliferation of prechondrocytes hypertrophy of osteoblasts, bone remodeling, and net mineralization [1].
- GH stimulates cartilage growth. This is most evident as a widening of the epiphyseal plate and is associated with an increase in amino acid incorporation into cartilage and bone [2]. GH also stimulates the uptake of sulfate by cartilage in vivo [3,4].
- GH deficiency results in alterations in the physiology of different systems of the body, manifesting as altered lipid metabolism, increased subcutaneous visceral fat, decreased muscle mass, decreased bone density, low exercise performance, and reduced quality of life.
Genetics
MOLECULAR GENETICS OF GROWTH HORMONE DEFICIENCY
30 percent of GHD is genetic [9,10].
The POU1F1 gene
is responsible for pituitary-specific transcription of genes for GH, prolactin, thyrotropin, and the growth hormone releasing hormone (GHRH) receptor [11,12].
PROP1 mutations result in failure to activate POU1F1/Pit1 gene expression and probably cause pituitary hypoplasia and/or familial multiple pituitary hormone deficiency [17]; paradoxical cystic hyperplasia of the pituitary also has been reported [18]. This is the most common known genetic cause of combined pituitary hormone deficiency [19,20].
GHRH receptor gene defects
Children with mutations in the GHRH receptor gene have undetectable GH release during standard provocative tests and after exogenous GHRH administration, but they respond to GH treatment.
Deletions and mutations of GH1
GH1 is the gene encoding GH, located on chromosome 17. Gene deletions, frameshift mutations, and nonsense mutations of GH1 have been described as causes of familial GHD [25].
Syndrome of bioinactive GH
A diagnosis of the syndrome of bioinactive GH has been proposed for short children with a phenotype that resembles that of isolated GHD, with normal or slightly elevated basal GH levels in combination with low insulin-like growth factor I (IGF-I) concentrations that increase after treatment with exogenous GH. True molecular abnormalities involving a mutant GH molecule have rarely been reported [26,27]
Laron syndrome
It is caused by homozygous or compound heterozygous mutations in the growth hormone (GH) receptor gene; a variety of mutations have been identified, most of which affect the extracellular GH-binding region of the receptor [2-4].
GH receptor signal transduction
a homozygous missense mutation in the gene encoding signal transducer and activator transcription 5B (STAT5B) which is essential for normal signaling of the GH receptor [15-18].
IGF-I gene mutations
Mutations in the gene encoding IGF-I cause a unique syndrome of GHD 21-23
patients with IGF-I gene mutations have prenatal growth failure, microcephaly, significant neurocognitive deficits, sensorineural hearing loss 21
Defective stabilization of circulating IGF-I
deficiency of acid-labile subunit (ALS) which is important for the stabilization of the IGF-I-IGFBP-3 complex, forming a three-part (ternary) complex in the circulation. [25,26].
IGF-I receptor mutations
Mutations in the gene encoding the receptor for IGF-I have been reported in infants presenting with pre- and postnatal growth failure [27-30].
These mutations are thought to result in partial loss of function of the IGF-I receptor