Angelman syndrome [遺伝・代謝]
What is Angelman syndrome?
Angelman syndrome is a complex genetic disorder that primarily affects the nervous system. Characteristic features of this condition include developmental delay, intellectual disability, severe speech impairment, and problems with movement and balance (ataxia). Most affected children also have recurrent seizures (epilepsy) and a small head size (microcephaly). Delayed development becomes noticeable by the age of 6 to 12 months, and other common signs and symptoms usually appear in early childhood.
Children with Angelman syndrome typically have a happy, excitable demeanor with frequent smiling, laughter, and hand-flapping movements. Hyperactivity and a short attention span are common. Most affected children also have difficulty sleeping and need less sleep than usual. Some affected individuals have unusually fair skin and light-colored hair.
With age, people with Angelman syndrome become less excitable, and the sleeping problems tend to improve. However, affected individuals continue to have intellectual disability, severe speech impairment, and seizures throughout their lives. Adults with Angelman syndrome have distinctive facial features that are described as "coarse." Some also develop an abnormal side-to-side curvature of the spine (scoliosis). The life expectancy of people with this condition appears to be nearly normal.
How common is Angelman syndrome?
Angelman syndrome affects an estimated 1 in 12,000 to 20,000 people.
What are the genetic changes related to Angelman syndrome?
Many of the characteristic features of Angelman syndrome result from the loss of function of a gene called UBE3A. People normally inherit one copy of the UBE3A gene from each parent. Both copies of this gene are turned on (active) in many of the body's tissues. In certain areas of the brain, however, only the copy inherited from a person's mother (the maternal copy) is active. This parent-specific gene activation is caused by a phenomenon called genomic imprinting. If the maternal copy of the UBE3A gene is lost because of a chromosomal change or a gene mutation, a person will have no active copies of the gene in some parts of the brain.
Several different genetic mechanisms can inactivate or delete the maternal copy of the UBE3A gene. Most cases of Angelman syndrome (about 70 percent) occur when a segment of the maternal chromosome 15 containing this gene is deleted. In other cases (about 11 percent), Angelman syndrome is caused by a mutation in the maternal copy of the UBE3A gene.
In a small percentage of cases, a person with Angelman syndrome inherits two copies of chromosome 15 from his or her father (paternal copies) instead of one copy from each parent. This phenomenon is called paternal uniparental disomy. Rarely, Angelman syndrome can also be caused by a chromosomal rearrangement called a translocation, or by a mutation or other defect in the region of DNA that controls activation of the UBE3A gene. These genetic changes can abnormally turn off (inactivate) UBE3A or other genes on the maternal copy of chromosome 15.
A deletion of a gene called OCA2 is associated with light-colored hair and fair skin in some people with Angelman syndrome. The OCA2 gene is located on the segment of chromosome 15 that is often deleted in people with this disorder. The protein produced from this gene helps determine the coloring (pigmentation) of the skin, hair, and eyes.
The causes of Angelman syndrome are unknown in 10 to 15 percent of affected individuals. Changes involving other genes or chromosomes may be responsible for the disorder in these individuals.
Read more about the OCA2 and UBE3A genes and chromosome 15.
Can Angelman syndrome be inherited?
Most cases of Angelman syndrome are not inherited, particularly those caused by a deletion in the maternal chromosome 15 or by paternal uniparental disomy. These genetic changes occur as random events during the formation of reproductive cells (eggs and sperm) or in early embryonic development. Affected people typically have no history of the disorder in their family.
Rarely, a genetic change responsible for Angelman syndrome can be inherited. For example, it is possible for a mutation in the UBE3A gene or in the nearby region of DNA that controls gene activation to be passed from one generation to the next.
Where can I find information about diagnosis, management, or treatment of Angelman syndrome?
These resources address the diagnosis or management of Angelman syndrome and may include treatment providers.
•Gene Review: Angelman Syndrome
•Gene Tests: Angelman Syndrome
•MedlinePlus Encyclopedia: Speech Disorders
You might also find information on the diagnosis or management of Angelman syndrome in Educational resources and Patient support.
To locate a healthcare provider, see How can I find a genetics professional in my area? in the Handbook.
Where can I find additional information about Angelman syndrome?You may find the following resources about Angelman syndrome helpful. These materials are written for the general public.
•MedlinePlus - Health information (3 links)
•Genetic and Rare Diseases Information Center - Information about genetic conditions and rare diseases
•Additional NIH Resources - National Institutes of Health (2 links)
•Educational resources - Information pages (11 links)
•Patient support - For patients and families (7 links)
You may also be interested in these resources, which are designed for healthcare professionals and researchers.
•Gene Reviews - Clinical summary
•Gene Tests - DNA tests ordered by healthcare professionals
•ClinicalTrials.gov - Linking patients to medical research
•PubMed - Recent literature
•Online Books - Medical and science texts
Scriver's Online Metabolic and Molecular Bases of Inherited Disease (OMMBID): Molecular Cytogenetics of Contiguous Gene Syndromes: Mechanisms and Consequences of Gene Dosage Imbalance
•OMIM - Genetic disorder catalog
What other names do people use for Angelman syndrome?
•AS
See How are genetic conditions and genes named? in the Handbook.
What if I still have specific questions about Angelman syndrome?
•Ask the Genetic and Rare Diseases Information Center.
•Submit your question to Ask the Geneticist.
Where can I find general information about genetic conditions?
The Handbook provides basic information about genetics in clear language.
•What does it mean if a disorder seems to run in my family?
•What is a chromosome?
•Can changes in the number of chromosomes affect health and development?
•Are chromosomal disorders inherited?
•What are genomic imprinting and uniparental disomy?
These links provide additional genetics resources that may be useful.
•Genetics and health
•Resources for Patients and Families
•Resources for Health Professionals
What glossary definitions help with understanding Angelman syndrome?
ataxia ; cell ; chromosome ; deletion ; developmental delay ; DNA ; egg ; embryonic ; gene ; hyperactivity ; imprinting ; maternal ; microcephaly ; mutation ; nervous system ; pigmentation ; protein ; rearrangement ; reproductive cells ; scoliosis ; seizure ; sign ; spectrum ; sperm ; symptom ; syndrome ; tissue ; translocation ; uniparental disomy
You may find definitions for these and many other terms in the Genetics Home Reference Glossary.
See also Understanding Medical Terminology.
References (12 links)
<参考>
http://ghr.nlm.nih.gov/condition/angelman-syndrome
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by ゴリゴリくん (2010-08-14 00:09)