Gene replacement therapy for Syngap1 Syndrome

Background
SYNGAP1 encodes the neuronal cytoplasmic protein SynGAP (SYNaptic GTPase Activating Protein), a regulatory protein involved in synaptic development, structure, function, and plasticity. Heterozygous mutations in SYNGAP1 gene lead to haploinsufficiency, resulting in a mental retardation-type 5 (MRD5), a disease characterised by intellectual disability (ID), developmental delay, epilepsy, autism spectrum disorder and other behavioural abnormalities. SYNGAP1 loss-of-function is one of the most common causes of ID with epilepsy.

Objectives
Given the remarkable pre-clinical and clinical efficacy mediated by adeno-associated virus serotype 9 (AAV9)1,2, our goal is to design and progress AAV9 gene therapy strategy for SYNGAP1 replacement towards proof-of-concept in pre-clinical model of MRD5. Our specific aims are: i) Design and evaluate therapeutic vectors; ii) Evaluate the in vitro efficacy of the therapeutic vector system in iPSC derived neurons; iii) complete a proof-of-concept efficacy stydy in pre-clinical in vivo model of MRD5.
Novelty
MRD5 patients currently have no treatment options. Our Syngap1 gene replacement strategy is an attractive solution since it is targeting the causative gene. No previous studies of syngap1 gene replacement therapy have been reported.

Experimental Approach
AAV vector design and production: Currently, the adeno-associated (AAV)-based system is one of the most refined and effective gene delivery systems. Remarkable safety and efficacy data were reported from 2 separate phase I/II clinical trials in patients with rare diseases1,3. We plan to design AAV encoding codon optimised human SYNGAP1 gene.
In vitro validation of the therapeutic vector using iPS-derived neurons from SYNGAP1 patients. A number of readouts will be used as demonstrated in a recent study utilising this cell model.4
Pilot in vivo study: This will be performed in wild type mice to assess transduction efficiency of the generated AAV vector and select the dose for pre-clinical study in MRD5 mouse model.
Pre-clinical proof-of concept using in vivo disease model. The efficacy of the selected AAV will then be tested in vivo using the well characterised Syngap1 heterozygous model (Syngap1+/-). Syngap1+/- model display significant phenotype recapitulating many features of the disease in humans.

Training opportunities
The student will join a team of several postdocs, PhD students and technicians. He/she will benefit from their support and expertise. The student will use/learn cell culture, basic molecular biology techniques, viral vector design, disease modelling, immunostaining, microscopy and in vivo pre-clinical expertise. Gene manipulation in the cell models will be achieved using lentiviral and adeno-associated vectors. The student will also be affiliated to the Gene Therapy Innovation and Manufacturing Centre (GTIMC). GTIMC is currently a DiMeN DTP Associate Partner. The newly established centre has signed an agreement with Cell & Gene Therapy Catapult allowing Technology Transfer of analytical assays to be used for gene therapy product characterisation. The Tech transfer is scheduled to start in January 2022. The student will use the assays to characterise the Syngap1 vectors generated under this project. He/She will generate data key to establish future partnerships with industry