[Source:  Medical News Today]
Most genes are inherited as two working copies, one from the mother and one from the father. However, in a few instances, a gene is imprinted, which means that one copy is silenced. This is called genomic imprinting. If the active copy is mutated, then disease results, even though the silenced gene copy may be normal.

Angelman syndrome, which causes learning difficulties, speech problems, seizures, jerky movements and an unusually happy disposition, results when a gene inherited from the mother in a particular area of chromosome 15 is mutated and the other copy of the gene, inherited from the father, is silenced. In a report that appears online in the journalNature¸ Dr. Arthur Beaudet, professor of molecular and human genetics at Baylor College of Medicine and a clinical geneticist at Texas Children’s Hospital, and colleagues answer the question: “Can we turn on the activity of the paternal gene?”

Angelman syndrome occurs when an infant inherits a mutated copy of the imprinted gene UBE3A from his or her mother. He or she also has a paternal copy of the gene, but it is silenced by a long ribbon of RNA called the UBE3A anti-sense transcript. (Antisense, in this case, is complementary to the ribbon of RNA, which means it binds to it and silences any activity.)

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