Functional analysis of epilepsy-linked pathogenic variants of the Munc18-1 gene in the inhibitory nervous system of Caenorhabditis elegans.

Heterozygous de novo mutations in Munc18-1, which is essential for neurotransmitter release, cause early infantile epileptic encephalopathy. Munc18-1-linked epilepsy is currently an untreatable disorder and its precise disease mechanism remains elusive. Here, we investigated how Munc18-1 pathogenic variants affect inhibitory neurons using Caenorhabditis elegans . Expression analysis revealed that three missense mutant proteins form aggregates in the cell body of gamma-aminobutyric-acid (GABA)-ergic motoneurons, resulting in a strong reduction of their expression in axons. Their defects of axonal expression correlated closely with pentylenetetrazol-induced convulsions, suggesting that the degree of instability of each mutant protein account for the severity of the epileptic phenotypes.