A de novo missense mutation of GABRB2 causes early myoclonic encephalopathy

Area of Science:

• Neuroscience
• Genetics
• Molecular Biology

Background:

• Early myoclonic encephalopathy (EME) is a severe neonatal neurological disorder characterized by seizures and myoclonus.
• Current understanding links EME to three genes with metabolic features.
• The genetic basis of EME, particularly involving ion channels, remains largely unexplored.

Purpose of the Study:

• To identify novel genetic causes of early myoclonic encephalopathy (EME).
• To investigate the functional consequences of identified mutations on gamma-aminobutyric acid-A (GABA_A) receptor function.
• To establish a link between ion channel dysfunction and EME pathogenesis.

Main Methods:

• Whole-exome sequencing of 214 patients with epileptic seizures using a 109-gene panel.
• Functional characterization of mutant gamma-aminobutyric acid-A (GABA_A) receptor subunits using electrophysiology and immunostaining in HEK293T cells.
• Analysis of mutation prevalence in EME and infantile spasms cohorts.

Main Results:

• A de novo heterozygous missense mutation (c.859A>C [p.Thr287Pro]) in GABRB2, encoding the beta2 subunit of the GABA_A receptor, was identified in an infant with EME.
• The identified GABRB2 mutation impaired GABA_A receptor trafficking to the cell membrane and reduced channel function, leading to a significant decrease in peak current amplitude.
• No GABRB2 mutations were found in other EME or infantile spasms cases, suggesting specificity.

Conclusions:

• A pathogenic mutation in the GABRB2 gene, affecting GABA_A receptor function, is a novel cause of early myoclonic encephalopathy (EME).
• The mutation's impact on GABAergic inhibition highlights the critical role of ion channel function in neonatal epilepsy.
• This finding expands the genetic landscape of EME and provides a potential target for future therapeutic strategies.