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Angelman syndrome

Angelman syndrome is a genetic condition characterized by developmental delays and neurological problems such as difficulty balancing and walking. It is caused by mutations in a gene in a particular region of chromosome 15.

Characteristics of Angelman syndrome
Angelman syndrome is a genetic condition that is typically associated with developmental delays, intellectual disability, speech impairment, movement disorder (unsteady walking or shakiness of the arms/legs) and a unique behavioral profile (happy personality, short attention span, hyperactivity, drooling, mouthing objects). Other features may include small head size (microcephaly), seizures, difficulty falling and staying asleep, crossing of the eyes (strabismus), curvature of the spine (scoliosis), reflux and constipation.

Diagnosis/Testing
The diagnosis of Angelman syndrome can be based upon clinical findings alone. Genetic testing is valuable for confirming the diagnosis and for providing genetic counseling. Angelman syndrome is caused by several different mechanisms that change the way the UBE3A gene is expressed on chromosome 15. The UBE3A gene is imprinted in brain cells. This means that the gene is expressed differently depending on from which parent it was inherited. The UBE3A gene is turned on (“active”) on the copy inherited from the mother and turned off (“inactive”) on the copy inherited from the father.
Approximately 70% of individuals with Angelman syndrome have a missing piece (deletion) on chromosome 15 that came from the mother. Another 11% of individuals with Angelman syndrome have a change or mutation in the UBE3A gene that came from the mother. Angelman syndrome can also be caused by paternal uniparental disomy (i.e., when both copies of chromosome 15 is received from the father instead of one copy from each parent). Finally, a small percentage of individuals with Angelman syndrome have a change in the imprinting center, which functions as a “switch” for the UBE3A gene. In these individuals, the UBE3A gene from the mother is present, but “turned off.”

Management/Surveillance
Management of Angelman syndrome includes early and frequent developmental intervention, including physical, occupational and speech therapies. These therapies should continue into adulthood to achieve functional potential. Due to the fact that individuals with Angelman syndrome tend to understand more than they can express, other methods of communication are encouraged (augmentative communication aids, sign language). Many young children with Angelman syndrome are in need of feeding therapy and are followed by a nutritionist. Individuals with Angelman syndrome should be monitored closely for growth/weight and scoliosis by their regular doctor. Seizures and sleep problems are often managed by a neurologist. A psychologist may be useful in managing problematic behaviors. Routine eye exams are recommended because of the risk of strabismus. Many individuals with Angelman syndrome are also in need of ankle/leg braces (orthotics) to help them walk.

Mode of inheritance
Angelman syndrome occurs in all populations around the world and affects girls and boys equally. Most cases of Angelman syndrome are sporadic, meaning that there are no other family members with Angelman syndrome.

Risk to family members
The chance for parents of a child with Angelman syndrome to have another affected child depends on the genetic cause. Most deletions, uniparental disomy, and imprinting center defects occur brand new (de novo) and are not inherited. Thus, the risk of other siblings being affected is low. However, some genetic causes can be inherited from the mother. For example, when a mother is found to carry the same UBE3A gene mutation or imprinting center defect found in her child with Angelman syndrome, the risk of having another child with Angelman syndrome is 50% with each pregnancy.

Special considerations
None

Resources
Angelman Syndrome Foundation
Genetics Home Reference: Angelman syndrome
Medical Home Portal: Angelman Syndrome

References
Dagli AI, Williams CA. (Updated 16 June 2011). Angelman Syndrome. In: GeneReviews at GeneTests Medical Genetics Information Resource (database online). Copyright, University of Washington, Seattle. 1997-2013. Available at http://www.ncbi.nlm.nih.gov/books/NBK1144/. Accessed [08/30/2013].
Williams, CA. et al. (2010)."Clinical and genetic aspects of Angelman syndrome." Genetics in Medicine 12(7): 385-395.
Williams, CA. et al. (2005)."Angelman syndrome 2005: Updated consensus for diagnostic criteria." American Journal of Medical Genetics Part A 140A(5): 413-418.

Created:08/2013

Updated:mm/yyyy

Created by:Christie Turcott, MS, CGC

Edited by:Seema Jamal, MSc, LCGC



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