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Insulin-like growth factor 2 (IGF-2), also called somatomedin A, is a hormone produced by the human body. This molecule receives its name from a chemical similarity to insulin. IGF-2 plays its most significant role in the process of gestation.
IGF-2 encourages cell division in a variety of tissues. It prepares the uterus for pregnancy and causes embryonic growth after conception has taken place. It exerts its function primarily by binding to the IGF-1 receptor. The hormone also binds to the IGF-2 receptor; the function of this receptor seems mostly to be clearing away IGF-2 molecules and returning them to the Golgi apparatus. There, they are packaged and prepared for reuse.
The gene for IGF-2 is imprinted with information about which allele came from which parent. The imprinting is accomplished with molecular tags that are added to the DNA. This process is controlled by a genetic sequence called imprinting center 1 (ICR-1), found nearby on chromosome 11. In practice, only the father's allele is expressed. Failure of this imprinting mechanism can cause over-expression of the protein and may be involved in several diseases.
Excess of IGF-2 is associated with various diseases, especially Beckwith-Wiedemann syndrome (BWS). BWS is a congenital condition involving hypoglycemia, excessive growth, and increased risk of cancer. These symptoms are predictable outcomes of IGF-2, which encourages cell growth and glucose usage. People who have this condition often display growth problems at birth because the condition is based on a problem with this specialized hormone. The risk for cancer usually only lasts for the first few years of life, so these people usually grow normally as children and adolescents. Some studies have found that BWS is more likely to occur when pregnancies are technologically assisted.
Overproduction of IGF-2 can also result from cancer. Doege-Potter syndrome is a condition of hypoglycemia—low blood sugar—resulting from overproduction of IGF-2 by tumor cells. Doege-Potter syndrome is fairly rare—even more rare than BWS—and only results from extremely large fibrous tumors. Removing the tumor eliminates the syndrome.
Russell-Silver syndrome, a growth disorder associated with dwarfism, may conversely result from a deficiency of IGF-2. Intermediate variations in height and weight, usually not characterized as pathological, can result from variations in the content and expression of the IGF-2 gene.
IGF-2 is often studied and discussed in conjunction with insulin-like growth factor 1 (IGF-1). Both of these molecules have similar structures and bind to the IGF-1 receptor. IGF-1 appears more often and has more direct connections to human growth hormones.
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