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Angelman Syndrome
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Angelman Syndrome (AS) was first reported in 1965 by Dr. Harry Angelman in England. Although case reports from the United States first began appearing in the medical literature in the early 1980s. In 1987, it was first noted that around half of the children with AS have a small piece of chromosome 15 missing.
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-related epigenetic imprinting; the biochemical mechanism is DNA methylation. In a normal individual, the maternal allele is expressed and the paternal allele is silenced. If the maternal contribution is lost or mutated, the result is Angelman syndrome. (When the paternal contribution is lost, by similar mechanisms, the result is Prader-Willi syndrome.) It should be noted that the methylation test that is performed for Angelman syndrome (a defect in UBE3A) is actually looking for the gene's neighbor SNRPN (which has the opposite pattern of methylation).
The following list features of Angelman Syndrome and their relative frequency in affected individuals.
- Developmental delay, functionally severe
- Speech impairment, none or minimal use of words; receptive and non-verbal communication skills higher than verbal ones
- Movement or balance disorder, usually ataxia of gait and/or tremulous movement of limbs
- Behavioral uniqueness: any combination of frequent laughter/smiling; apparent happy demeanor; easily excitable personality, often with hand flapping movements; hypermotoric behavior; short attention span
The diagnosis of Angelman syndrome is based on:
- A history of delayed motor milestones and then later a delay in general development, especially of speech
- Unusual movements including fine tremors, jerky limb movements, hand flapping and a wide-based, stiff-legged gait.
- Characteristic facial appearance (but not in all cases).
- A history of epilepsy and an abnormal EEG tracing.
- A happy disposition with frequent laughter
- A deletion on chromosome 15
Diagnostic criteria for the disorder were initially established in 1995 in collaboration with the Angelman Syndrome Foundation.
Those with the syndrome are generally happy and contented people, who like human contact and play. People with AS exhibit a profound desire for personal interaction with others. Communication can be difficult at first, but as a child with AS develops, there is a definite character and ability to make themselves understood. It is widely accepted that their understanding of communication directed to them is much larger than their ability to return conversation. Most afflicted people will not develop more than 5-10 words, if any at all.
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