Ipscs - A Platform To Study Autism Spectrum Disorder

Abstract

Recent genetic studies have demonstrated that a significant amount of the liability to develop autism traces to rare mutations at a single locus, some of which are de novo, and CNVs. Genetic variations in hundreds of genes have been implicated. However, no individual cause accounts for more than 1% of ASD cases. Few, if any, of the variants are specific to the core ASD phenotype. Many are associated with other disorders, most often epilepsy and intellectual handicap, suggesting significant overlap in the etiology of these disorders. In addition to rare alleles of major effect, association studies suggested involvement of numerous common variants with smaller effects. Together, these studies underscore that ASD risk likely involves many different genes and distinct modes of inheritance among individuals. Developing animal models of autism will be extremely difficult. Core symptoms of ASD, including deficits in social communication, imagination and curiosity are difficult to model well in other organisms. Mechanisms underlying ASDs need to be studied in human patients and in cells that share the genetic background of these patients. Currently, studying neurons derived from human induced pluripotent stem cells (hiPSCs) is the only viable method of studying live developing neurons from ASD patients, with their genetic background maintained. In the last decade, our group has identified cellular and molecular phenotypes for rare but highly penetrant forms of ASD such as Timothy Syndrome. Phelan-McDermid Syndrome, and 22q11 deletion syndrome. Our results and those from other laboratories suggest that on a transcriptomic level ASD associated genes have some overlapping functions and converge on downstream regulatory pathways and are involved in altered synaptic structure and disrupted neuronal differentiation. Due to the cost, labor, and expertise needed to derive and functionally characterize neurons from hiPSCs, to date, very few have examined idiopathic forms of ASD, and the number of cell lines investigated has been very small. As part of an effort funded by the California Institute for Regenerative Medicine (CIRM) our group at Stanford recruited 300 individuals with ‘idiopathic’ ASD including matched controls into a hiPSC biobank. This effort provides unique opportunities to compare results obtained by studying neurons derived from patients with rare but highly penetrant forms of ASD to those derived from patients with ‘idiopathic’ ASD.