Correction of Autism Risk Gene Expression Levels using CRISPR-Activation

Autism Spectrum Disorder (ASD) is a neurodevelopmental disorder that has a substantial genetic component to its risk. In fact, about 20% of cases harbor mutations of major effect that are newly arising in germ cells (sperm or egg) and not carried in the parents’ own cellular DNA (de novo mutations). The majority of these mutations are either known to or predicted to lead to the loss of one copy of the gene (of the two normally inherited). This in turn leads to disease through a condition called haploinsufficiency; a condition in which a single copy of a functional gene is not enough to maintain normal function. We propose to correct the effects of these mutations by activating the non-mutant copy to restore the gene to near normal levels.

We do this by leveraging advances in gene editing technology – using CRISPR-A to target regions of DNA known as enhancers that will turn up the expression of genes that cause ASD. We will target these so-called enhancers (a region of DNA that increases the likelihood of a gene’s expression) in stem cell-based 3D human cultures called cortical organoids, which have been shown to replicate many early features of brain development. CRISPR-A uses a non-gene editing form of CRISPR to bind a transcriptional co-activator to an enhancer, thus turning on the target gene. This takes advantage of native DNA elements that control gene expression without editing the genome or relying on artificial gene constructs for overexpression.

We have demonstrated the effectiveness of this approach on cells in culture by using CRISPR-A to increase expression of CHD8 and SCN2A in human cortical organoids established from stem cells with haploinsufficient mutations. This rescue of expression additionally rescued certain ASD-associated characteristics specific to each mutation; these characteristics are also observed in individuals with mutations in the same genes. This provides strong evidence for the efficacy of this approach. In work that is funded by the Eagles Autism Foundation, we are partnering with Dr. Alex Nord at UC Davis and Dr. Ethan Goldberg at Children’s Hospital of Philadelphia to translate this work into mouse models of autism, to further determine the potential of CRISPR-A as a therapy.