Autism spectrum disorder (ASD) is caused by both environmental and genetic factors, with the genetic contribution estimated at 60-80%. Dozens of genes that increase risk for ASD have been identified, most based on de novo mutations, but these mutations are predicted to account for only 15-20% of ASD cases. Thus, the majority of the genetic contribution to ASD is predicted to result from common and rare inherited variation, but few such genes have been identified. Recently, using whole genome sequencing, we reported genome wide evidence for >60 ASD risk genes, 26 of them novel for ASD, with signals derived from inherited and de novo protein truncating or missense mutations. The functions of most of these genes are unknown, so a crucial and necessary next step is to explore their impact on neurodevelopment and neuronal function using a model organism. The current pace of translating genetic risk factors into phenotypes, mechanisms and therapies is limited in part by inefficiencies with in vivo mammalian model systems, which makes them impractical for creating and behaviorally testing large numbers of mutant lines. Here, we leverage the zebrafish, which occupies a unique niche as a vertebrate model with features amenable to both in vivo screening and mechanistic understanding, including ex utero development, transparency, small size, rapid development, a conserved yet relatively simple vertebrate brain, behaviors relevant to ASD, and cost-effectiveness relative to mammalian models. While the zebrafish cannot recapitulate ASD and has limitations for modeling a human disorder, an emerging literature supports the notion that it is a useful model to study the functions of genes that contribute to ASD risk. Rather than assess ASD-risk genes one at a time, we will accelerate progress towards mechanistic understanding via high-throughput assays and analyses.
In Specific Aim 1 we will generate null mutations in the zebrafish orthologs of 24 high confidence, novel, genome-wide significant ASD risk genes, and systematically test each mutant for neurodevelopmental, behavioral, neuronal network, and transcriptomic phenotypes.
In Specific Aim 2, we will use transcriptomic analyses, at the whole brain and single cell levels, to integrate ASD risk genes into functional networks, and test for convergence across genes and species, including ASD post mortem brain. We will also test for functional associations among behavioral phenotypes that are often co-morbid in ASD, such as disrupted sleep and social behavioral deficits.
In Specific Aim 3 we will perform mechanistic studies to understand how mutation of specific ASD-risk genes leads to phenotypes. This project will efficiently and cost-effectively create and characterize vertebrate animal models for a large number of novel ASD risk genes. These animal models will be a valuable resource for the community, particularly for large-scale in vivo drug screens to identify new therapies for ASD.
Autism spectrum disorder (ASD) is caused by both environmental and genetic factors, but most of the genes responsible for ASD remain unknown, and the functions of most ASD risk genes that have been identified are poorly understood. We will use zebrafish as a vertebrate model system to study the effects of a large number of recently-identified ASD risk genes on brain development and behavior. These studies will improve our understanding of why mutations in specific genes result in ASD and may ultimately lead to novel therapies.
