Angelman syndrome is a genetic disorder. It's most often caused by problems with a gene located on chromosome 15 called the ubiquitin-protein ligase E3A (UBE3A) gene.

Genes are segments of DNA that provide the blueprints for all of your characteristics. You receive your genes, which occur in pairs, from your parents. One copy comes from your mother (maternal copy), and the other copy comes from your father (paternal copy).

A missing or defective gene

Both genes in a pair usually are active. This means that your cells use information from both the maternal copy and the paternal copy of each gene pair. But in a small number of genes, only one copy of a gene pair is active. The activity of each gene copy depends on whether it was passed from your mother or from your father. This parent-specific gene activity is called imprinting. In these genes, when the copy that's usually active is missing or defective, it causes problems in the functions and characteristics controlled by that gene.

Normally, only the maternal copy of the UBE3A gene is active in the brain, caused by what's known as genomic imprinting. Most cases of Angelman syndrome occur when part of the maternal chromosome 15, which contains this gene, is missing or damaged. In a small number of cases, Angelman syndrome is caused when two paternal copies of the gene are inherited, instead of one paternal and one maternal copy (paternal uniparental disomy).

Jan. 17, 2012