Epilepsy in Angelman syndrome: A scoping review

Abstract

Angelman Syndrome (AS) is characterized by severe developmental delays including marked speech impairment, movement abnormalities(ataxia, tremor), and unique behaviors such as frequent laughter and is caused by dysfunctional maternal UBE3A gene (maternal 15q11-13 deletions, maternal specific UBE3A mutation, uniparental disomy, and imprinting defect). Intractable epileptic seizures since early childhood with characteristic EEG abnormalities are present in 80-90% patients with AS. Underlying pathophysiology may involve neocortical and thalamocortical hyperexcitability secondary to severe reduction of GABAergic input, as well as dysfunctional synaptic plasticity, deficient synaptogenesis, and neuronal morphological immaturity. The onset of epilepsy is most prevalent between 1 and 3 years of age; however, approximately 25% of patients developed epilepsy before one year of age. Various types of generalized seizures are most prevalent, with most common types are myoclonic and atypical absence.More than 95% of epilepsy patients may have daily seizures at least for a limited time during early childhood, and two-third patients develop disabling seizures. Fever provoked seizures, and frequent occurrence of nonconvulsive status epilepticus are two unique features. Seizures are frequently pharmacoresistant. Considering underlying prominent GABAergic dysfunction, clinicians had used AEDs that target GABAergic signaling such as valproate, phenobarbital, and clonazepam as first-line therapies for AS. However, due to the unfavorable side effect profile of these AEDs, a recent treatment approach involves priority use of levetiracetam, clobazam, topiramate, lamotrigine, ethosuximide, VNS, and carbohydrate-restricted diets. Besides symptomatic management, there has been recent progress to find a curative treatment with the following approaches: 1. Gene/protein replacement therapy (Adeno and lentiviral vector therapy to deliver a gene or secretory protein); 2. Activation of the intact but silent paternal copy of UBE3A (antisense oligonucleotide therapy and artificial transcription factors); and 3. Downstream therapies (OV101/gaboxadol, ketone supplement, novel compounds/peptides, anti-inflammatory/regenerative therapy).

Keywords: Angelman syndrome; Epilepsy; Gene therapy; Molecular therapy; UBE3A; seizures, EEG.

Fig 1.

Representative EEG showing posterior dominant 3–4 Hz notched delta and theta activities (black arrow) and anterior dominant, rhythmic 2–3 Hz activities intermixed with spike-wave discharges(red arrow).

Fig. 2.

MRI of a child with Angelman syndrome at the age of 8 months. Myelination on T1w(left) shows still deficient frontal and temporal white matter and a hypoplastic corpus callosum corresponding to a maturation stage of 5–6 months. T2w image(right) indicates mildly widened ventricles, dorsally thin corpus callosum, a slightly patchy T2 signal of the white matter with particular prominence over the parieto-occipital region.

Fig 3.

Current and potential future therapies in Angelman syndrome