Angelman syndrome
| Angelman syndrome | |
|---|---|
 |
|
| "Boy with a Puppet" or "A child with a drawing" by Giovanni Francesco Caroto. | |
| Pronunciation | /ˈeɪndʒəlmən/ |
| Classification and external resources | |
| Specialty | medical genetics |
| ICD-10 | Q93.5 |
| ICD-9-CM | 759.89 |
| OMIM | 105830 |
| DiseasesDB | 712 |
| MedlinePlus | 007616 |
| MeSH | D017204 |
| GeneReviews | |
| Orphanet | 72 |
Angelman syndrome (AS) is a neurodevelopmental disorder characterized by severe intellectual and developmental disability, sleep disturbance, seizures, jerky movements (especially hand-flapping), frequent laughter or smiling, and usually a happy demeanor.
AS is a classic example of genomic imprinting in that it is caused by deletion or inactivation of genes on the maternally inherited chromosome 15 while the paternal copy, which may be of normal sequence, is imprinted and therefore silenced. The sister syndrome, Prader–Willi syndrome, is caused by a similar loss of paternally inherited genes and maternal imprinting.
AS is named after a British pediatrician, Harry Angelman, who first described the syndrome in 1965. An older, alternative term for AS, "happy puppet syndrome", is generally considered pejorative and stigmatizing so it is no longer the accepted term. People with AS are sometimes referred to as "angels", both because of the syndrome's name and because of their youthful, happy appearance.
The following text lists signs and symptoms of Angelman syndrome and their relative frequency in affected individuals.
Angelman syndrome is caused by the loss of the normal maternal contribution to a region of chromosome 15, most commonly by deletion of a segment of that chromosome. Other causes include uniparental disomy, translocation, or single gene mutation in that region. A healthy person receives two copies of chromosome 15, one from the mother, the other from the father. However, in the region of the chromosome that is critical for Angelman syndrome, the maternal and paternal contribution express certain genes very differently. This is due to sex-specific epigenetic imprinting; the biochemical mechanism is DNA methylation. In a normal individual, the maternal allele of the gene UBE3A, part of the ubiquitin pathway, is expressed and the paternal allele is specifically silenced in the developing brain. In the hippocampus and cerebellum, the maternal allele is almost exclusively the active one. If the maternal contribution is lost or mutated, the result is Angelman syndrome. (Some other genes on chromosome 15 are maternally imprinted, and when the paternal contribution is lost, by similar mechanisms, the result is Prader-Willi syndrome.) The methylation test that is performed for Angelman syndrome (a defect in UBE3A) looks for methylation on the gene's neighbor SNRPN (which is silenced by methylation on the maternal copy of the gene).
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