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ATP Investigators Undertake Comprehensive Brain Tissue Analysis

November 14, 2007

The Autism Tissue Program (ATP) Tissue Advisory Board recently approved five exciting new projects, marking the most comprehensive study of brain tissue in autism research to date. These studies highlight the use of donated brain tissue to explore new and provocative hypotheses about the causes of autism and shape thinking about treatment strategies.

Autism Genome Project Brain Tissue Genotyping Initiative

PI: Stephen W. Scherer, the Hospital for Sick Children

The international Autism Genome Project Consortium (AGP) proposes to perform genome-wide genotyping and copy number variation (CNV) analysis. The study will be carried out using ATP supplied tissue. This project is aimed at generating a resource of information for other tissue users. The AGP has already characterized 1,100 subject families with multiple autistic family members to identify and then remove those genetic samples with copy number variation, allowing improved genetic study of the remaining areas of DNA which predispose to autism. The benefits of this study will be to discover new genetic variants associated with ASD (including genes, mutations, rearrangements and CNVs), create novel diagnostic tests for individuals and families, identify new biochemical or developmental pathways, and potential stratification of families as high and low genetic risk.

Role of MET-kinase and CASPR2 in Autism

PI: Andrew West, University of Alabama at Birmingham

Recent molecular genetics data spotlight two candidate genes, MET-kinase and CASPR2, as containing potential genetic variation associated with autism susceptibility. Using recently developed and highly specific antibodies capable of assessing the function of MET-kinase and CASPR2, coupled with new techniques to amplify partially degraded nucleic acid from brain samples, this project will help determine whether MET-kinase, CASPR2 or related protein products may serve as pathologic diagnostic indicators of ASD, and help to solidify the role of these proteins in autism susceptibility. New pathways for targeted therapeutic intervention arise with such identification. A second goal of this proposal is to complete a genotype of each sample and deposit the data into public databases that will add to the information from the Genome Project Initiative.

Serotonin Neurons in Postmortem Autism Brains

PI: Efrain Azmitia, Professor, New York University

This study tests the hypothesis that interruption or disorder of certain serotonin fibers in the brain are an early indicator of regional abnormality or pathology. The association of serotonin with autism is based on drug response, genetic association with serotonin-transporter gene mutations, peripheral blood levels and animal models. Still, little is known about serotonin in postmortem brains. The goals of the project are to study the serotonergic brain cells by visualizing them using a specific serotonin transporter protein antibody. Various characteristics of these specific brain cells, including shape, fiber organization, and density of connections will be recorded and statistically compared to non-autistic brain tissue. Understanding the exact alterations of serotonin fibers will help in better understanding of the disorder and, consequently, facilitate the development of effective treatment strategies.

Comparative Analysis of Cerebellar Neuropathology in Human Autistic Patients and Cerebellar Mutant Mice

PI: Margaret Bauman, Boston University School of Medicine

Neuroanatomical and neuroimaging studies conducted by different research groups on brains of autistic subjects show faulty brain development. Amongst all brain regions affected by autism, the cerebellum is a particularly interesting research target. In contrast to the forebrain, its structure is highly conserved in mammalian evolution, and its development takes place mainly during late pregnancy and early postnatal life (a period believed to be of critical significance in autism). A common anatomical finding is a reduced number of Purkinje cells in the cerebellum of autistic subjects. The Purkinje cell is a type of brain cell with a wide influence on many motor and non-motor regions of the brain and spinal cord. In essence, all aspects of behavior are influenced by this particular type of neuron. Importantly, the reduced numbers of Purkinje cells in autism has been traced back to the prenatal period. Purkinje cells are known to be sensitive to sex hormones (gonadal steroids), particularly estrogens, which promote their development and survival. Also, Purkinje cells themselves are known to synthesize neurosteroids (steroid hormones produced within the brain). Preliminary data strongly suggest that Reelin, an autism candidate gene, interacts with estrogens during mouse cerebellar development. In male mice, a deficit of Reelin leads to reduced numbers of Purkinje cells, while in female mice, Purkinje cells may be protected from the Reelin deficit by high estrogen concentrations. This phenomenon may explain, in part, the higher male prevalence of autism. The team seeks to find supporting evidence of an interaction between gonadal steroids and development of the autistic cerebellum in humans.

Metabolomics of Human Embryonic Stem Cells and Neural Precursors: A Humanized Model to Discover Biomarkers and Biochemical Pathways of Autism

PI: Gabriela Cezar, University of Wisconsin-Madison

This project addresses a critical limitation in the attempt to unravel the causes of autism: the inability to perform in utero studies of human brain cell development, and the accompanying biochemical/metabolic pathways which might give rise to autism. The work will be done by a very promising young investigator with extensive experience in the stem cell research field. This research endeavor is essentially crossing her experience over into the proteomic (metabolomic) field of autism research. The study is exciting for several reasons. The PI has provided very strong preliminary evidence for a cellular model in which to test out most of her hypotheses (in this case measurement of kynurenine, glutamate, and GABAergic metabolites) using human embryonic stem (hES) cells that are differentiated into neural precursors and neurons. The PI will test these expression profiles in brain tissue accrued from controls and autism subjects by previous ATP researcher Dr. Vogel, exemplifying the kind of collaboration and sharing of tissue resources that we encourage.