Angelman Syndrome: Causes, Symptoms and Treatment

What is Angelman Syndrome?

Angelman syndrome is a rare genetic neurological disorder first described by British pediatrician Harry Angelman in 1965. It affects approximately 1 in 12,000 to 20,000 people and is characterized by severe intellectual disability, developmental delays, and distinctive neurological and behavioral features. Affected individuals often display a notably happy, excitable demeanor with frequent smiling and laughter, which is why the condition was historically referred to as Happy Puppet Syndrome -- a term no longer used due to its insensitive connotations.

Causes

Angelman syndrome is caused by the loss of function of the UBE3A gene located on chromosome 15q11-q13. In the brain, UBE3A is exclusively expressed from the maternal (mother-inherited) copy of the gene. The following genetic mechanisms can lead to the condition:

• Deletion: Approximately 70% of cases result from a missing segment of the maternal chromosome 15 (15q11-q13).
• Uniparental disomy (UPD): The child inherits both copies of chromosome 15 from the father, with no maternal copy present (approx. 7% of cases).
• Imprinting defect: An error in the genomic imprinting pattern prevents expression of the maternal UBE3A gene (approx. 3% of cases).
• UBE3A point mutation: A direct mutation within the UBE3A gene itself (approx. 11% of cases).
• Unknown cause: In a small proportion of cases, no genetic cause can be identified.

Symptoms

The signs of Angelman syndrome typically become noticeable within the first year of life, although a formal diagnosis is often not made until between the ages of 2 and 5.

Core Features

• Severe intellectual disability and developmental delay
• Absent or severely limited speech development (most affected individuals do not develop spoken language)
• Movement and balance difficulties (ataxia, tremulous limb movements, jerky gait)
• Epilepsy (affecting approximately 80% of individuals, often difficult to control)
• Frequent laughing and smiling, with an excitable, sociable temperament
• Hyperactivity and short attention span
• Sleep disturbances with reduced need for sleep
• Microcephaly (smaller than normal head circumference) in many cases
• Characteristic EEG patterns (abnormal brain wave activity)

Physical Features

• Fair skin and light hair (particularly in deletion cases)
• Wide-set eyes (hypertelorism)
• Wide mouth with widely spaced teeth

Diagnosis

Diagnosis of Angelman syndrome is based on clinical findings and confirmed through molecular genetic testing:

• Clinical assessment: Evaluation of developmental history, behavior, and neurological signs by a specialist (pediatric neurologist or clinical geneticist).
• DNA methylation analysis: Detects deletions, UPD, and imprinting defects (identifies approximately 80% of cases).
• FISH or chromosomal microarray analysis: Used to detect deletions on chromosome 15.
• UBE3A gene sequencing: Used to identify point mutations in the UBE3A gene.
• EEG (electroencephalogram): Shows characteristic patterns that may support the diagnosis.

Treatment

There is currently no cure for Angelman syndrome. Treatment is symptomatic and focuses on improving quality of life and supporting development.

Medical Treatment

• Antiepileptic drugs (AEDs): To manage seizures -- commonly used agents include valproic acid, clonazepam, levetiracetam, and topiramate. Carbamazepine and vigabatrin are generally avoided as they may worsen seizure activity in Angelman syndrome.
• Melatonin: To improve sleep quality and duration.

Therapeutic Interventions

• Speech and language therapy: Focused on developing communication skills, often using augmentative and alternative communication (AAC) methods.
• Physiotherapy: To improve motor function, balance, and gait.
• Occupational therapy: To support daily living skills and fine motor development.
• Early intervention and special education: Individualized educational programs tailored to the needs of each child.

Research and Future Therapies

Ongoing research is investigating ways to reactivate the silenced paternal copy of UBE3A in order to restore gene function. Approaches include antisense oligonucleotides (ASOs) and gene therapy strategies. Several clinical trials are currently underway and show promising early results.

Prognosis and Long-term Outlook

Angelman syndrome is a lifelong condition. Life expectancy is generally not significantly reduced. Seizure frequency may decrease in some individuals as they enter adulthood. Communication abilities and mobility can be supported and improved through consistent therapy. However, most affected individuals require ongoing support with daily living throughout their lives.

References

1. Williams CA et al. - Angelman syndrome 2005: updated consensus for diagnostic criteria. American Journal of Medical Genetics, 2006; 140(5): 413-418.
2. Buiting K, Williams C, Horsthemke B. - Angelman syndrome - insights into a rare neurogenetic disorder. Nature Reviews Neurology, 2016; 12(10): 584-593.
3. Orphanet: Angelman Syndrome. Available at: https://www.orpha.net (accessed 2024).