Mutations in DEPDC5, NPRL2 and NPRL3, which make up the GATOR1 complex, have been found in a cohort of families with focal epilepsy. However the mechanisms of how these cause the disease remains elusive. In vitro studies have shown that GATOR1 functions to inhibit mTOR signalling and hyperactivity of this pathway has independently been linked with epilepsy. mTOR dysregulation is therefore hypothesised to be the major factor in the pathology of GATOR1-related epilepsy. We have developed a functional assay using CRISPR null cell lines where the null phenotype of hyperactive mTOR can be rescued by expressing the wildtype protein. GATOR1 mutations found in patients can therefore be screened for loss-of-function in the context of mTOR. Multiple germline mutations have been confirmed to have lost this function partially or completely. Somatic GATOR1 mutations have also been identified in patients and can be screened to investigate a ‘second-hit’ mechanism of disease, where seizures are proposed to result from a second somatic mutation in the brains of germline heterozygotes. To further investigate this hypothesis, we established a conditional mouse model for Depdc5. Using CRISPR, we generated a floxed allele which, following the unilateral electroporation of Cre into developing brains, recombines to result in discrete regions of null tissue. Preliminary results show increased mTOR signalling and increased soma size in regions where the gene function has been abolished. Together, data from investigations using cell lines and mutant mice support the involvement of mTOR dysregulation in GATOR1-related epilepsy and a second-hit mechanism of disease.