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.
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 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, 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 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 may be described as "coarse." Other common features include unusually fair skin with light-colored hair and an abnormal side-to-side curvature of the spine (scoliosis). The life expectancy of people with this condition appears to be nearly normal.
The following text lists signs and symptoms of Angelman syndrome and their relative frequency in affected individuals.
- Developmental delay, functionally severe
- Speech impairment, no 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
Frequent (more than 80%):
- Delayed, disproportionate growth in head circumference, usually resulting in microcephaly (absolute or relative) by age 2
- Seizures, onset usually < 3 years of age
- Abnormal EEG, characteristic pattern with large amplitude slow-spike waves
- Hypopigmented skin and eyes
- Tongue thrusting; suck/swallowing disorders
- Hyperactive tendon reflexes
- Feeding problems during infancy
- Uplifted, flexed arms during walking
- Prominent mandible
- Increased sensitivity to heat
- Wide mouth, wide-spaced teeth
- Sleep disturbance
- Frequent drooling, protruding tongue
- Attraction to/fascination with water
- Excessive chewing/mouthing behaviors
- Flat back of head
- Smooth palms
- Abnormality of the tongue
- Behavioral abnormality
- Broad-based gait
- Cerebral cortical atrophy
- Cognitive impairment
- Mandibular prognathia
- Muscular hypotonia
Many of the characteristic features of Angelman syndrome result from mutations in chromosome 15, which encodes 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. 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.
In a small percentage of cases, Angelman syndrome results when a person inherits two copies of chromosome 15 from his or her father (paternal copies) instead of one copy from each parent.
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.
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 cases.
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 or inactivity on chromosome 15 by array comparative genomic hybridization (aCGH) or by BACs-on-Beads technology.
The severity of the symptoms associated with AS varies significantly across the population of those affected. Some speech and a greater degree of self-care are possible among the least profoundly affected. Unfortunately, walking and the use of simple sign language may be beyond the reach of the more profoundly affected. Early and continued participation in physical, occupational (related to the development of fine-motor control skills), and communication (speech) therapies are believed to improve significantly the prognosis (in the areas of cognition and communication) of individuals affected by AS. Further, the specific genetic mechanism underlying the condition is thought to correlate to the general prognosis of the affected person. On one end of the spectrum, a mutation to the UBE3A gene is thought to correlate to the least affected, whereas larger deletions on chromosome 15 are thought to correspond to the most affected. The clinical features of Angelman syndrome alter with age. As adulthood approaches, hyperactivity and poor sleep patterns improve. The seizures decrease in frequency and often cease altogether and the EEG abnormalities are less obvious. Medication is typically advisable to those with seizure disorders. Often overlooked is the contribution of the poor sleep patterns to the frequency and/or severity of the seizures. Medication may be worthwhile in order to help deal with this issue and improve the prognosis with respect to seizures and sleep. Also noteworthy are the reports that the frequency and severity of seizures temporarily escalate in pubescent AS girls but do not seem to affect long-term health. The facial features remain recognizable but many adults with AS look remarkably youthful for their age. Puberty and menstruation begin at around the average age. Sexual development is thought to be unaffected, as evidenced by a single reported case of a woman with Angelman syndrome conceiving a female child who also had Angelman syndrome. The majority of those with AS achieve continence by day and some by night. Dressing skills are variable and usually limited to items of clothing without buttons or zippers. Most adults are able to eat with a knife or spoon and fork and can learn to perform simple household tasks. General health is fairly good and life-span near average. Particular problems which have arisen in adults are a tendency to obesity (more in females), and worsening of scoliosis, if it is present. The affectionate nature which is also a positive aspect in the younger children may also persist into adult life where it can pose a problem socially, but this problem is not insurmountable.
There is currently no cure available. The epilepsy can be controlled by the use of one or more types of anticonvulsant medications. However, there are difficulties in ascertaining the levels and types of anticonvulsant medications needed to establish control, because AS is usually associated with having multiple varieties of seizures, rather than just the one as in normal cases of epilepsy. Many families use melatonin to promote sleep in a condition which often affects sleep patterns. Many individuals with Angelman syndrome sleep for a maximum of 5 hours at any one time. Mild laxatives are also used frequently to encourage regular bowel movements, and early intervention with physiotherapy is important to encourage joint mobility and prevent stiffening of the joints. Speech and Language Therapy is commonly employed to assist individuals with Angelman syndrome and their communication issues.
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. People with AS tend to develop strong non-verbal skills to compensate for their limited use of speech. 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.
Seizures are a consequence, but so is excessive laughter,which is a major hindrance to early diagnosis.