The seizures of Angelman syndrome patients are dynamic in nature and may change with age. While myoclonic seizures usually happen in early childhood, adolescents and young adults mainly have nonepileptic myoclonus, according to a retrospective study.
Myoclonic seizures are the primary and most common type of seizures experienced by Angelman patients. These are characterized by brief, sudden movements of one or a group of muscles, and can be accompanied by the loss of an acquired function.
Adult Angelman syndrome patients may also develop another type of seizure called nonepileptic myoclonus, which are not linked to hyperelectrical activity of the brain in electroencephalogram (EEG) tests (exams that record the electrical activity of the brain).
The records of 185 Angelman patients, 102 (55%) of them males and 83 (45%) of them females, ages 1 to 44, were analyzed for myoclonic seizures and episodes of nonepileptic myoclonus.
A history of myoclonic seizures was seen in about 15% of all individuals. This type of seizure began before patients reached the age of 8 and had a similar distribution between genders: 55% in males and 44% in females.
Nonepileptic myoclonus seizures occurred in 35 people (19%) from the two Mass General programs. Their ages ranged from 11 to 44, equally affecting males (51%) and females (49%).
The prevalence of nonepileptic myoclonus seizures appeared to increase with age and was not present in patients before the age of 10 (the age of onset varied from 10 to 26).
Nonepileptic myoclonus seizures can be difficult to treat and patients often don’t respond to medication. However, researchers found that clobazam (brand names Onfi, Frisium); levetiracetam (marketed as Keppra); and clonazepam (brand name Klonopin, Rivotril, Navotrax) were effective in some individuals.
These results suggest that while myoclonic seizures are linked to electrical changes in EEG tests and occur frequently in young children with Angelman syndrome, “nonepileptic myoclonus typically begins in adolescence or early adulthood and has no electroencephalogram (EEG) correlate, alteration in consciousness, or regression, but can significantly impact quality of life,” researchers wrote.
“Larger, prospective studies are needed to further characterize these events and assess potential treatments,” they added.