Current and emerging treatment options for Angelman syndrome

Drug Treatments for Neurodevelopmental Disorders: Targeting Signaling Pathways and Homeostasis

PURPOSE OF THE REVIEW

Preclinical and clinical evidence support the notion that neurodevelopmental disorders (NDDs) are synaptic disorders, characterized by excitatory-inhibitory imbalance. Despite this, NDD drug development programs targeting glutamate or gamma-aminobutyric acid (GABA) receptors have been largely unsuccessful. Nonetheless, recent drug trials in Rett syndrome (RTT), fragile X syndrome (FXS), and other NDDs targeting other mechanisms have met their endpoints. The purpose of this review is to identify the basis of these successful studies.

RECENT FINDINGS

Despite increasing evidence of disruption in synaptic homeostasis, most genetic variants associated with NDDs implicate proteins involved in cell regulation and not in neurotransmission. Metabolic processes, in particular mitochondrial function, appear to play a role in NDD pathophysiology. NDDs are also characterized by distinctive cell signaling abnormalities, which link cellular and synaptic homeostasis. Recent successful trials in NDDs, including those of trofinetide, the first drug specifically approved for one of these disorders (i.e., RTT), implicate the targeting of downstream processes (i.e., signaling pathways) rather than neurotransmitter receptors. Recent positive drug studies in NDDs and their underlying mechanisms, in conjunction with new knowledge on the pathophysiology of these disorders, support the concept that targeting signaling and cellular and synaptic homeostasis may be a preferred approach for ameliorating synaptic abnormalities in many NDDs.

Precision Medicine in Angelman Syndrome

Angelman syndrome (AS) is a rare neurogenetic disorder caused by a loss of function of UBE3A on the maternal allele. Clinical features include severe neurodevelopmental delay, epilepsy, sleep disturbances, and behavioral disorders. Therapy currently evolves from conventional symptomatic, supportive, and antiseizure treatments toward alteration of mRNA expression, which is subject of several ongoing clinical trials.This article will provide an overview of clinical research and therapeutic approaches on AS.

Neural hyperexcitability in Angelman syndrome: Genetic factors and pharmacologic treatment approaches

Angelman syndrome (AS) is a rare neurodevelopmental disorder that is typically caused by deletion or a loss-of-function mutation of the maternal copy of the ubiquitin ligase E3A (UBE3A) gene. The disorder is characterized by severe intellectual disability, deficits in speech, motor abnormalities, altered electroencephalography (EEG) activity, spontaneous epileptic seizures, sleep disturbances, and a happy demeanor with frequent laughter. Regarding electrophysiologic abnormalities in particular, enhanced delta oscillatory power and an elevated excitatory/inhibitory (E/I) ratio have been documented in AS, with E/I ratio especially studied in rodent models. These electrophysiologic characteristics appear to relate with the greatly elevated rates of epilepsy in individuals with AS, and associated hypersynchronous neural activity. Here we briefly review findings on EEG, E/I ratio, and epileptic seizures in AS, including data from rodent models of the disorder. We summarize pharmacologic approaches that have been used to treat behavioral aspects of AS, including neuropsychiatric phenomena and sleep disturbances, as well as seizures in the context of the disorder. Antidepressants such as SSRIs and atypical antipsychotics are among the medications that have been used behaviorally, whereas anticonvulsant drugs such as valproic acid and lamotrigine have frequently been used to control seizures in AS. We end by suggesting novel uses for some existing pharmacologic agents in AS, including noradrenergic transmission reducing drugs (alpha2 agonists, beta blockers, alpha1 antagonists) and cholinesterase inhibitors, where these various classes of drugs may have the ability to ameliorate both behavioral disturbances and seizures.