Biological correlates of altered brain growth in autism

Yale University, New Haven CT

Investigators

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Abstract

DESCRIPTION (provided by applicant): A consistently replicated biological phenotype in autism spectrum disorders (ASD) is a larger head circumference (HC) in the first years of life. We hypothesize that increased brain size in ASD is attributable to altered dynamics of cell proliferation and/or differentiation due to genetic changes intrinsic to neural cells. In this application, we will derive induced pluripotent stem cells (iPSC) from skin fibroblasts in individuals with ASD and typically developing children with macrocephaly. Whole genome studies examining structural genetic variation in DNA isolated from iPSC as compared to lymphocytes of the same individuals will ensure genetic stability of the reprogrammed cells. In Specific Aim 1, iPSC lines obtained from 23 participants with ASD and 11 typically developing individuals with macrocephaly will be characterized with respect to cell proliferation, cell survival and genome wide structural variation such as copy number variations (CNVs) by paired end mapping (PEM) and array capture and sequencing. In Specific Aim 2, genome wide CNV as well as sequence variation datasets will be obtained in blood lymphocyte DNA taken from the same 23 participants with ASD and 11 typically developing individuals, plus a limited number of their family members. This will involve (1) PEM (2) array capture for exons and promoter regions with sequencing, and (3) genome-wide mapping of retroelement patterns. Genetic regions potentially important for ASD that will emerge from this study will be validated by targeted resequencing in two larger, independent cohorts of ASD probands and their family members, each comprising about 500 individuals. The immediate goal of our project is to create a new resource and analytical tool. The genetic studies comparing DNA sequence variation in iPSC and blood samples are essential to establish that the iPSC genomic structure corresponds to that identified in the patients. In future studies, iPSC lines generated in this project will be specifically differentiated along the neural lineage and further analyzed with respect their proliferation, differentiation and survival, allowing us to test whether increased brain size in ASD is attributable to altered dynamics of cell proliferation and/or differentiation. These neural cells derived from iPSC lines will be characterized at the transcript and epigenetic levels, for which the basic characterization proposed in this project will provide a necessary platform. Our ultimate goal is to link neurobiological phenotypes and changes in gene expression during the neural differentiation process, with the underlying genetic structure of the individuals to elucidate disease pathogenesis. Therefore, the proposed project will provide a resource for correlating, in future studies, genomic sequence, regulation and intensity of gene expression, cellular (biological) consequences, and patient behavior. PUBLIC HEALTH RELEVANCE: This project will develop lines of pluripotent cells (iPSC) from individuals with autism spectrum disorders (ASD) with macrocephaly and typically developing children, using cells obtained by a skin biopsy. We will produce several iPSC lines per individual and characterize them with respect to their biology and their structural genetic variation. The aim is create a resource and analytical tool, which will allow us to examine neuronal differentiation in autism spectrum disorders.