Growth Hormone Disorders
There are numerous conditions associated with alterations of growth hormone production or receptor recognition.
Too little Growth Hormone or Deficiency
Childhood–Dwarfism: Dwarfism results if the liver and other target tissues are not sufficiently stimulated by growth hormone. This condition arises because either too little growth hormone is produced during childhood, or because the growth hormone receptors expressed by cells are non-functional. Under conditions where the growth hormone receptor isn’t functioning properly, IGF-1 levels are low relative to growth hormone.
Mental retardation is also commonly observed in cases of growth hormone deficiency (GHD). Other symptoms of GHD resemble the normal aging process.
Adulthood–Growth Hormone Deficiency (GHD): Adult onset GHD is characterized by reduced lean body mass, bone density and strength, while visceral fat and mortality, principally due to cardiovascular disease, increases. A characteristic elevation in plasma cholesterol (high LDL/low HDL) is most likely responsible for the increased incidence of cardiovascular disease in GHD patients. Insulin resistance is also frequently encountered. This condition frequently results from the medical intervention of a Pituitary tumor with resultant loss of the growth hormone producing cells, or Somatotropes.
Adulthood–Normal Aging: We are all familar with the belly that “often” forms in males after the age of 30 year. This increase in body fat is in large part due to an age-dependent decrease in growth hormone.
The reduction in growth hormone with age is associated with increased body fat, and reduced muscle mass and bone density. This is a clinical condition referred to as Somatopause. Other aspects of the normal aging process that is correlated with a reduction of growth hormone are cardiovascular disease, wrinkling, gray hair, decreased energy, and reduced sexual function. Many of these same symptoms are present in younger adults with GHD.
Too Much Growth Hormone or Overabundance
Too much growth hormone can have different effects depending on the age at which it occurs. Alarmingly, reduced life expectancy is frequently encountered in natural disorders where growth hormone levels are abnormally elevated.
Childhood–Giagantism: An overabundance of growth hormone during childhood or adolescence gives rise to giagantism. It is a very rare condition that usually results from a tumor of the cells that produce growth hormone.
Adulthood–Acromegaly: Acromegaly results from an excess of growth hormone (ie, IGF-1) during adulthood. IGF-1 is responsible for longitudinal growth (increase in height) during childhood and adolescence. However, an excess of IGF-1 during adult life (after our bones have stopped elongating) causes bones to widen and increase in girth. This disfigures our features, particularly in the face (large square jaw), hands and feet.
Glucose intolerance is also commonly observed in acromegliacs. In fact, about one quarter of all acromegliacs develop diabetes mellitus due to peripheral resistance to insulin.
Growth Hormone Replacement Therapy
This is a field that is still in its infancy. Previously, human growth hormone was isolated directly from the anterior pituitary of cadavers. This approach yielded extremely small amounts of painfully expensive growth hormone. With the recent advent of genetic engineering, recombinant growth hormone can now be produced more economically in bacteria. Although this has reduced the cost considerably, it is still expensive.
Use in Growth Hormone Deficiency (GHD)…
Children: GHD in children is most noticeably characterized by stunted growth. Recombinant growth hormone is often used in children with GHD to augment growth.
Adults: Increases in bone density and lean body mass are often observed in patients with adult-onset GHD when treated with recombinant growth hormone. Plasma cholesterol has also been observed to stabilize (low LDL/high HDL).
Use in Normal Individuals…
Elderly: Some studies have shown that recombinant growth hormone treatment in the elderly may actually reverse some of these signs of aging. In particular, an increase in lean body mass is commonly observed. In some cases a reduction in serum cholesterol is also documented. Unfortunately, adverse side effects are also sometimes encountered and may include edema, fluid retention and carpal tunnel syndrome.
Athletes: In adults recombinant growth hormone has been shown to increase lean body mass. This has led to the notion that growth hormone might be used to enhance physical performance in athletes. Interestingly, although growth hormone treatment in adults frequently increases lean body mass, increases in strength are more difficult to prove. Furthermore, fluid retention and enlargement of some internal organs contribute significantly to the observed increase in lean body mass. Finally, it is still an open issue whether the use of recombinant growth hormone causes acromegaly in athletes.
Conceicao F.L., Bojensen A., Lunde Jorgensen J.O., Christiansen J.S. (July 2001) Growth hormone therapy in adults. Frontiers in Neuroendocrinology Volume 22 (3): pages 213-246.
Growth Hormone: Physiologic Effects of Growth Hormone.