Loss of function mutations in the Synaptic GTPase Activating Protein 1 (SYNGAP1) cause a neurodevelopmental disorder characterized by intellectual disability, epilepsy and autism. The mutations in SYNGAP1 are believed to result in reduced protein abundance in neurons by about 50%. Studies in mice have suggested that normalizing SynGAP abundance improves symptoms from loss of function mutations.

We are undertaking a genome-wide, cell based screen to identify genes that when depleted increase SynGAP abundance. Using a sgRNA/Cas9 library, we are targeting over 19,000 genes with greater than 70,000 guide RNAs in our screen. Using fluorescently tagged SynGAP, we sorted cells with increased SynGAP abundance using flow cytometry followed by next generation sequencing of the barcoded sgRNAs to identify those enriched in cells with greatest increase in SynGAP abundance. The candidate hits that we identify from this primary screen will be rigorously validated ultimately in neurons differentiated from induced pluripotent stem cells (iPSCs) derived from patients with SYNGAP1 mutations.

We have completed the primary screen and are currently identifying those genes whose protein products regulate SynGAP stability. We have created iPSCs from patients with SYNGAP1 mutations. Induced neurons from these patients have increased spike frequency and burst number compared with controls.

Induced neurons from patients with pathogenic SYNGAP1 mutations have increased neuronal excitability mimicking the epileptiform discharges seen in patients by electroencephalography.

Ultimately, we aim to discover a targeted therapy for patients with SYNGAP1 mutations that increases SynGAP abundance and normalizes neuronal activity.