Biallelic variants in the synaptic vesicle glycoprotein 2 A are associated with epileptic encephalopathy.

Synaptic Vesicle Glycoprotein 2 A (SV2A) is a membrane protein of synaptic vesicles and the binding site of antiepileptic drug levetiracetam. Biallelic Arg383Gln is reported in a family with intractable epilepsy earlier. Here, we report on the second family with early onset drug resistant epilepsy. We identified homozygous Arg289Ter variant by exome sequencing that segregated with the phenotype in the family. The affected children in these two families are normal at birth and developed recurrent seizures beginning in the second month of life and developed secondary failure of growth and development. Knock out mice models earlier had replicated the human phenotype observed in these two families. These findings support that biallelic loss of function variants in SV2A result in early onset intractable epilepsy in humans.