How Does Human Growth Hormone Make Children Taller?

"You have to do your own growing no matter how tall your grandfather was," said Abraham Lincoln, the 16th U.S. president, who brought about the emancipation of the slaves. Lincoln, of course, was speaking metaphorically, but taken literally, some children cannot abide by Lincoln's words. They have a growth hormone deficiency which, if left untreated, will prevent them from doing their own growing. Researchers have known for some time that growth hormone can be effective in treating deficient children. More recently Swedish scientists discovered that growth hormone can also help healthy children with a short stature grow taller.

Growth Hormone

Growth hormone is a protein that signals growth. Its prime construction site is the pituitary gland, or hypophysis, a pea-sized endocrine gland at the base of the brain. But the hormone is also produced in the hippocampus, a center for memory, according to a report by a research team in the March, 2006 issue of "PNAS." The protein is encoded in five gene segments on the SHOX gene in the genome. M-RNA, a messenger genetic molecule, copies the five gene segments and carries the structure to a different location in the cell. Here protein building blocks, called "amino acids," are linked together in the right order to form the hormone. Defective growth hormone is the result of a splicing error or a mistake in genetic coding.

How Growth Hormone Works

Growth hormone released from the pituitary gland triggers the release of a second growth hormone called insulin-like growth factor-1, or IGF-1. The two hormones bind to cell receptors in bone, muscle and other tissue. Here they signal growth or increased cell division. For the bones to grow, bone cells must also add minerals, such as calcium and phosphate. McGill professor of pediatrics Harvey Guyda emphasizes the importance of testing for both growth hormone and IGF-1 when determining whether a child has a growth hormone deficiency.

Growth Hormone Deficiency

Growth hormone deficiency is a medical condition that leads to inadequate production of intact growth hormone. Heidelberg University professor Gudrun Rappold and her team report that a frequent trigger of increased amounts of defective growth hormone is a mutation in the SHOX gene or a defect in the gene's regulation. We all have about 1 percent of defective growth hormone. But people with growth hormone deficiency have 10 to 50 percent, according to Vanderbilt professor of biological sciences James Patton. The more defective material a child has, the slower he grows. Defective growth hormone cannot stimulate growth itself, and it also hinders activity of normal growth hormone.

Growth Hormone to Adjust Height

Human growth hormone can be prescribed legally only for three conditions: Growth hormone deficiency that causes short stature in children, adult growth hormone deficiency due to rare pituitary tumors and muscle-wasting disease in AIDS patients. However, a new study led by Goteborg professor of pediatrics Kestin Albertsson-Wikland shows that even when a child is not growth hormone deficient, growth hormone therapy can increase her final height. The researchers saw a mean gain of more than three inches, and in some cases they found a gain of nearly eight inches.

Gene Therapy

A team of Vanderbilt researchers discovered a new type of gene therapy, called "RNA interference," which can reverse genetic growth hormone deficiency in mice. When the team inserted a gene coding for defective growth hormone into the mice genome, the mice didn't grow normally. But when the mice also received RNA that interfered with the defective hormone's production, they restored to normal size, according to team member professor John Phillips. RNA interference has not yet been tested in humans.