Angelman Syndrome is a genetic disorder that affects the nervous system; this is a rare condition which is sometimes called the "happy puppet" syndrome because children with Angelman's Syndrome may look and move in ways similar to a puppet controlled by a string. The children have epilepsy, learning difficulties, severe speech delay, jerky movements, tongue-thrusting, a characteristic facial appearance and a happy mood with sudden bursts of laughter. Angelman syndrome is caused by the absence of certain genes normally presents on the copy of chromosome 15 inherited from the mother.
What is Chromosome 15?.
Humans normally have 46 chromosomes in each cell, divided into 23 pairs. Two copies of chromosome 15, one copy inherited from each parent, form one of the pairs. Chromosome 15 spans more than 102 million DNA building blocks (base pairs) and represents more than 3 percent of the total DNA in cells.
Angelman syndrome results from a loss of gene activity (expression) in a specific part of chromosome 15 in each cell. This region is located on the long (q) arm of the chromosome and is designated 15q11-q13. This region contains a gene called UBE3A that, when absent, likely causes the characteristic neurologic features of Angelman syndrome.
People normally inherit one copy of the UBE3A gene from each parent, and both copies of this gene are turned on in many of the body's tissues. In certain areas of the brain, however, only the copy inherited from a person's mother (maternal copy) is active. This parent-specific gene activation results from a phenomenon called genomic imprinting. If the maternal copy is lost because of a chromosomal change or a gene absent, a person will have no working copies of the UBE3A gene in some parts of the brain.
In most cases, Angelman syndrome results from a deletion in the maternal copy of chromosome 15. This chromosomal change deletes the region of chromosome 15 that includes the UBE3A gene.