Many cases of autism spectrum disorder (ASD) are caused by reduced expression of dosage-sensitive genes. A straightforward therapeutic approach is to virally supplement ASD risk genes to correct genetic dosage. However, the inevitable genetic overexpression in many cells induced by existing methods could overshoot and cause toxicity. Our ability to quantitatively control the level of therapeutic gene expression at the single-cell level is very limited, because the amount of virus varies substantially between individual cells, antithetical to the precision demanded by ASD gene therapies.

To address these issues, Wei-Hsiang Huang, in collaboration with Xiaojing Gao (Stanford University), propose to achieve quantitative, single-cell consistency of genetic overexpression using synthetic circuits that consist of biomolecules engineered to regulate each other and buffer against vector variability. The team is uniquely positioned to engineer these biomolecular circuits, given their experience in constructing post-transcriptional and post-translational circuits¹. Circuits based on post-transcriptional and post-translational control can be compactly delivered as a single transcript encoded on a vector and operate robustly regardless of the cellular context as long as the components are expressed at a reasonable level.

The key to dosage consistency is a feedback loop, where an overexpressed mRNA can repress its own expression. The team plans to build a circuit where the mRNA of ASD risk genes activates an intermediate protein, which then suppresses the CRISPR activation of the ASD gene. They will validate and optimize circuit components, especially mRNA-responsive protein expression. Each component will be assembled into the feedback circuits and optimize their dosage-control performance in vitro and in vivo, with the assistance of computational simulation. The circuit’s therapeutic potential will be evaluated in vivo using mouse models of ASD. This work will offer a potential way to manage cases of ASD associated with genetic haploinsufficiency and demonstrate the feasibility of a novel, quantitative form of gene therapy.