IGF2

The IGF2 gene provides instructions for making a protein called insulin-like growth factor 2. This protein plays an essential role in growth and development before birth. Studies suggest that insulin-like growth factor 2 promotes the growth and division (proliferation) of cells in many different tissues. Although the IGF2 gene is highly active during fetal development, it is much less active in the adult body.

People inherit one copy of most genes from their mother and one copy from their father. Both copies are typically active, or "turned on," in cells. For the IGF2 gene, however, the copy that is inherited from a person's father is the only active copy in most parts of the body. This sort of parent-specific difference in gene activation is caused by a phenomenon called genomic imprinting.

IGF2 is part of a cluster of genes on the short (p) arm of chromosome 11 that undergo genomic imprinting. Another gene in this cluster, H19, is also involved in growth and development. A nearby region of DNA known as imprinting center 1 (ICR1) or the H19 differentially methylated region (H19 DMR) controls the parent-specific genomic imprinting of both the H19 and IGF2 genes.

Beckwith-Wiedemann syndrome - associated with the IGF2 gene

Beckwith-Wiedemann syndrome often results from changes in a process called methylation that affects the ICR1 region. In genes that undergo genomic imprinting, the parent of origin is often marked, or "stamped," on the gene during the formation of egg and sperm cells. This stamping process, called methylation, is a chemical reaction that attaches small molecules called methyl groups to certain segments of DNA.

In some people with Beckwith-Wiedemann syndrome, the ICR1 region has too many methyl groups attached (hypermethylation). Because the ICR1 region controls the genomic imprinting of the H19 and IGF2 genes, this abnormality disrupts the regulation of both genes. Specifically, hypermethylation of the ICR1 region leads to a loss of H19 activity and increased activity of the IGF2 gene in many tissues. A loss of H19 gene activity, which normally restrains growth, and an increase in IGF2 gene activity, which promotes growth, together lead to overgrowth and an increased risk of tumors in people with Beckwith-Wiedemann syndrome.

In a few cases, Beckwith-Wiedemann syndrome has been caused by deletions of a small amount of DNA from the ICR1 region. Like abnormal methylation, these deletions disrupt the activity of the H19 and IGF2 genes.

cancers - associated with the IGF2 gene

Increased activity of the IGF2 gene has been associated with many types of cancer. Normally, the IGF2 gene undergoes genomic imprinting and only the copy inherited from a person's father is active. In some cancers, however, both the paternal and the maternal copies of the gene are active, increasing the amount of insulin-like growth factor 2 that cells can produce. This phenomenon is known as loss of imprinting (LOI). An increased amount of insulin-like growth factor 2 may stimulate the growth of tumor cells and prevent damaged cells from being destroyed.

Loss of imprinting of the IGF2 gene has been identified in several types of cancer known as embryonal tumors. These tumors include a rare form of kidney cancer called Wilms tumor, a cancer of muscle tissue called rhabdomyosarcoma, and a form of liver cancer called hepatoblastoma. Although these tumors commonly occur in people with Beckwith-Wiedemann syndrome, loss of imprinting of the IGF2 gene has also been seen in people with these tumors who do not have Beckwith-Wiedemann syndrome.

Loss of imprinting of the IGF2 gene has also been found in many other types of cancer, including cancer of blood-forming cells (leukemia) and cancers of the breast, prostate, lung, colon, and liver. Researchers suspect that this genetic change may someday be used to help predict a person's risk of developing these forms of cancer.

Russell-Silver syndrome - associated with the IGF2 gene

Changes in methylation of the ICR1 region are also responsible for some cases of Russell-Silver syndrome. The changes are different than those seen in Beckwith-Wiedemann syndrome and have the opposite effect on growth.

In Russell-Silver syndrome, the ICR1 region often has too few methyl groups attached (hypomethylation). Hypomethylation of the ICR1 region leads to a loss of IGF2 activity and increased activity of the H19 gene in many tissues. A loss of IGF2 gene activity, which normally promotes growth, and an increase in H19 gene activity, which restrains growth, together lead to poor growth and short stature in people with Russell-Silver syndrome.

other disorders - associated with the IGF2 gene

Normal variations (polymorphisms) in the IGF2 gene may be involved in determining adult height and/or weight. These polymorphisms are changes in single protein building blocks (amino acids) used to make insulin-like growth factor 2. Several studies have found associations between polymorphisms in the IGF2 gene and a person's body mass index (a measure of weight in relation to height). Research has also suggested that IGF2 polymorphisms may be a possible risk factor for eating disorders such as anorexia nervosa, bulimia nervosa, and binge eating disorder. Not all studies, however, have supported these associations. Many genetic and environmental factors determine weight and height, and more research is necessary to determine what effect, if any, polymorphisms in the IGF2 gene have on these characteristics.