Investigation of the molecular and cellular mechanisms of oligogenic inheritance in Autism spectrum disorder

Abstract

One of the greatest challenges in autism spectrum disorder (ASD) research is to identify the combinations of genetic variants required for determining disease causality and understand how the risk variants interact and converge on causative neurobiological pathways. Recently, through whole-exome sequencing (WES) of 291 Brazilian individuals with ASD and their parents, we identified in one individual with ASD rare compound heterozygous missense variants in the RELN gene, and a de novo splice site variant in the CACNA1H gene. RELN encodes Reelin, a secreted glycoprotein that controls neuronal migration and synapse functioning, and CACNA1H encodes the ±¹ subunit of the Cav3.2 T-type calcium channel that regulates neuronal excitability. Using induced pluripotent stem cell-derived neural progenitor cells from this individual with ASD and from control individuals, we showed that the variants in RELN and CACNA1H are deleterious and that there is an abnormal interaction between these mutated genes via the mTORC1 signaling pathway. Furthermore, after re-analyzing our WES data and analyzing the whole-genome sequencing (WGS) data from a larger cohort of individuals with ASD, the MSSNG cohort composed of 5,102 individuals with ASD and their parents, we found that the concomitant occurrence of rare deleterious variants in both alleles of genes for the Reelin cascade and in at least one allele of genes for calcium channels is significantly enriched in individuals with ASD (p=0.004), in an oligogenic inheritance model. However, it is still unknown how these mutated genes alter brain development and lead to ASD. The main objectives of this project are to explore: i) specific cell types and cellular phenotypes in the brain affected by the synergistic action of RELN and CACNA1H disruptive variants and those that are unique to either one of the alleles by using CRISPR-Cas9 gene editing and brain organoids; ii) the combinations of risk variants in individuals with ASD that follow the oligogenic inheritance model through the analysis of WES and WGS data from large cohorts of individuals with ASD. The results of this project will provide further insight into the mechanisms of gene interactions and combinations of variants required to cause ASD. (AU)