Angelman syndrome can result when a baby inherits both copies of a section of chromosome #15 from the father (rather than 1 from the mother, and 1 from the father). AS can also occur, even when chromosome #15 is inherited normally—1 chromosome coming from each parent.
Angelman syndrome is a complex genetic disorder that primarily affects the nervous system. Characteristic features of this condition include delayed development, intellectual disability, severe speech impairment, and problems with movement and balance (ataxia). Most affected children also have recurrent seizures (epilepsy) and 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.
Angelman syndrome is caused by a genetic mutation on chromosome 15. The name of this gene is UBE3A. Normally, people inherit one copy of the gene from each parent, and both copies become active in many areas in the body. Angelman syndrome occurs when only one copy of the gene is active in certain areas of the brain.
Children with Angelman syndrome typically have a happy, excitable demeanor with frequent smiling, laughter, and hand-flapping movements. Hyperactivity, a short attention span, and a fascination with water are common. Most affected children also have difficulty sleeping and need less sleep than usual.
With age, people with Angelman syndrome become less excitable, and 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 may be described as “coarse.” Other common features include unusually fair skin with light-colored hair and abnormal side-to-side curvature of the spine (scoliosis). The life expectancy of people with this condition appears to be nearly normal.
Angelman syndrome affects males and females in equal numbers. The prevalence of Angelman syndrome is estimated to be approximately 1 in 12,000-20,000 people in the general population. However, many cases may go undiagnosed making it difficult to determine the disorder’s prevalence in the general population.