Human Growth Hormone
Article updated and reviewed by Hubert Chen, MD, Associate Director of Medical Sciences, Amgen Inc. and Assistant Professor of Clinical Medicine University of California, San Francisco on May 10, 2005.
Human growth hormone is a protein secreted by the pituitary gland in the brain. Growth hormone, as the name implies, is essential for the growth and development of babies and children. However, growth hormone also plays a role in regulating various body functions in adults. Too much or too little growth hormone, therefore, can result in medical problems.
What Happens If There Is Too Much Growth Hormone?
The effect of too much growth hormone depends on the age of the individual. When the condition occurs in children (before growth plates in the skeleton have closed), it causes gigantism, which is characterized by tall stature.
In adults, the condition of excess growth hormone is called acromegaly. Because the growth plates have closed in adults, too much growth hormone does not cause one to grow taller. Instead, the condition is characterized by enlarged hands and feet, coarse facial features and growth of “skin tags”. Excess growth hormone may also cause diabetes, result in the formation of polyps (precursors of tumors) in the large intestine and increase heart size. All these undesirable effects of excess growth hormone contribute to the increased mortality in acromegaly.
What Happens If There Is Too Little Growth Hormone?
The effect of too little growth hormone also depends on the age of the individual. In children, growth hormone deficiency results in growth retardation, characterized by short stature, delayed secondary tooth eruption and delayed puberty.
In adults, growth hormone deficiency causes an increase in fat tissues and a decrease in muscle mass. In addition, growth hormone deficiency may negatively affect functioning of the heart (decreased cardiac output) or skeletal muscle (physical weakness). However, common (and perhaps major) complaints in adults may be lethargy and decreased sense of well-being that are frequently attributed to “old age”.
What Else Do I Need To Ask About If I Have A Growth Hormone Disorder?
Growth hormone disorders can occur as an isolated condition or in combination with abnormalities in other pituitary hormones. In the latter case, the secretion of one or more of the following hormones may be affected: corticotropin (ACTH), thyroid-stimulating hormone (TSH), luteinizing hormone (LH), follicle-stimulating hormone (FSH) or prolactin. When a growth hormone disorder is diagnosed, it is critical to make sure that the other pituitary hormones are being secreted properly.
Growth hormone deficiency, whether alone or in association with other abnormalities, is hereditary in about 10 percent of all cases.
Congenital hypopituitarism, a rare form of GH deficiency, may be genetic and frequently is fatal if not diagnosed in the neonatal period.
Secondary GH deficiency can occur due to central nervous system tumors, trauma, surgery involving the hypothalamus or pituitary gland in the brain or radiation.
Idiopathic (unknown cause) GH deficiency accounts for most cases.
Physical signs of GH deficiency may not be apparent at birth, but by the age of six months, growth retardation is obvious. In children, inspection may reveal short stature, delayed secondary tooth eruption and delayed puberty.
Those with isolated GH deficiency may have normal body proportions. Determination of bone age from hand X-rays is important in evaluating growth problems, as is the careful recording of height, and weight over time on any of several available growth charts.
Evaluation of the sella turcica (a saddle like prominence on the upper surface of the sphenoid bone in the brain) with CT (Computed Tomography) or MRI (Magnetic Resonance Imaging) is indicated to rule out calcification and neoplasms. In addition, the sella is abnormally small in 10 to 20 percent of children with pituitary GH deficiency.
Growth deficiency in adulthood tends to cause mild to moderate obesity, weakness (asthenia), and reduced cardiac output.
Blood tests are required to make the diagnoses. When growth hormone excess is suspected, a “suppression” test is used to determine whether growth hormone secretion from the pituitary gland can be appropriately decreased after a glucose load. Failure to suppress would be consistent with a diagnosis of gigantism or acromegaly.
Conversely, when growth hormone deficiency is suspected, a “provocative test” is done to determine whether growth hormone secretion can be appropriately stimulated after pharmacological stimulation (with either insulin or clonidine). Failure to stimulate would be consistent with a diagnosis of growth hormone deficiency.
Blood measurements of insulin-like growth factor 1 (IGF-1), a protein that reflects growth hormone activity, may be used as a screening or diagnostic test. In addition, imaging studies (with CT or MRI) are typically performed to make sure that there are no structural abnormalities involving the pituitary gland.
Because excess growth hormone conditions are typically caused by pituitary tumors, the definitive treatment usually involves surgical removal of the hyperactive tumor cells. Radiation and/or medications (pegvisomant, somatostatin analogs, dopamine agonists) may also be required to control excess growth hormone action.
Replacement therapy with synthetic human growth hormone (somatropin) is recommended for all children with short stature and documented growth hormone deficiency. Although the benefits of treating GH deficiency in children are well recognized, the value of treating growth hormone deficiency in adults appears less clear. There is concern that improvements in body composition and functional capacity may not be worth the financial cost or side effects of growth hormone treatment. Common side effects include hand swelling and stiffness, joint and muscle ache, and insulin resistance. In addition, there are reports linking increased cancer risks with increased growth hormone activity/IGF-1 levels in population studies. Although a causal relationship remains to be proven, these reports suggest that the risk-to-benefit ratio of treating growth hormone deficiency in adults needs to be more precisely determined. As a result, most physicians are conservative in initiating growth hormone therapy in adults.
Editorial review provided by VeriMed Healthcare Network.