ubiquitin protein ligase E3A
The UBE3A gene provides instructions for making a protein called ubiquitin protein ligase E3A. Ubiquitin protein ligases are enzymes that target other proteins to be broken down (degraded) within cells. These enzymes attach a small protein called ubiquitin to proteins that should be degraded. Cellular structures called proteasomes recognize and digest these ubiquitin-tagged proteins. Protein degradation is a normal process that removes damaged or unnecessary proteins and helps maintain the normal functions of cells.
Studies suggest that ubiquitin protein ligase E3A plays a critical role in the normal development and function of the nervous system. However, its exact role in nervous system cells is unclear.
People normally inherit two copies of the UBE3A gene, one from each parent. Both copies of the gene are turned on (active) in most of the body's tissues. In certain areas of the brain, however, only the copy inherited from a person's mother (the maternal copy) is active. This parent-specific gene activation results from a phenomenon known as genomic imprinting.
A loss of UBE3A gene function in the brain likely causes many of the characteristic features of Angelman syndrome, a complex genetic disorder that primarily affects the nervous system. This loss of function results from a chromosomal change or gene mutation that affects the maternal copy of the gene.
Several different genetic mechanisms can turn off (inactivate) or delete the UBE3A gene. Most cases of Angelman syndrome (about 70 percent) occur when a segment of the maternal chromosome 15 containing this gene is deleted. In another 11 percent of cases, Angelman syndrome results from mutations within the UBE3A gene itself. Most of these mutations lead to the production of an abnormally short, nonfunctional version of ubiquitin protein ligase E3A. Because the copy of the gene inherited from a person's father (the paternal copy) is normally inactive in some areas of the brain, loss of the maternal copy prevents any of the enzyme from being produced in these brain regions. This lack of enzyme function likely causes the major signs and symptoms of Angelman syndrome.
Other abnormalities involving the region of chromosome 15 that contains the UBE3A gene can also cause Angelman syndrome. These chromosomal changes include rearrangements (translocations) of genetic material or a defect in the region of DNA that controls activation of the UBE3A gene. Like mutations within the gene, these chromosomal changes prevent any functional ubiquitin protein ligase E3A from being produced in certain parts of the brain.
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