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Tero Toivanen

NIMH · Our brains are made of the same stuff, despite DNA differences - 1 views

  • “Having at our fingertips detailed information about when and where specific gene products are expressed in the brain brings new hope for understanding how this process can go awry in schizophrenia, autism and other brain disorders,” said NIMH Director Thomas R. Insel, M.D.
  • Among key findings in the prefrontal cortex:Individual genetic variations are profoundly linked to expression patterns. The most similarity across individuals is detected early in development and again as we approach the end of life.Different types of related genes are expressed during prenatal development, infancy, and childhood, so that each of these stages shows a relatively distinct transcriptional identity. Three-fourths of genes reverse their direction of expression after birth, with most switching from on to off.Expression of genes involved in cell division declines prenatally and in infancy, while expression of genes important for making synapses, or connections between brain cells, increases. In contrast, genes required for neuronal projections decline after birth – likely as unused connections are pruned.By the time we reach our 50s, overall gene expression begins to increase, mirroring the sharp reversal of fetal expression changes that occur in infancy.Genetic variation in the genome as a whole showed no effect on variation in the transcriptome as a whole, despite how genetically distant individuals might be. Hence, human cortexes have a consistent molecular architecture, despite our diversity.
  • Among key findings:Over 90 percent of the genes expressed in the brain are differentially regulated across brain regions and/or over developmental time periods. There are also widespread differences across region and time periods in the combination of a gene’s exons that are expressed.Timing and location are far more influential in regulating gene expression than gender, ethnicity or individual variation.Among 29 modules of co-expressed genes identified, each had distinct expression patterns and represented different biological processes. Genetic variation in some of the most well-connected genes in these modules, called hub genes, has previously been linked to mental disorders, including schizophrenia and depression.Telltale similarities in expression profiles with genes previously implicated in schizophrenia and autism are providing leads to discovery of other genes potentially involved in those disorders.Sex differences in the risk for certain mental disorders may be traceable to transcriptional mechanisms. More than three-fourths of 159 genes expressed differentially between the sexes were male-biased, most prenatally. Some genes found to have such sex-biased expression had previously been associated with disorders that affect males more than females, such as schizophrenia, Williams syndrome, and autism.
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  • Our brains are all made of the same stuff. Despite individual and ethnic genetic diversity, our prefrontal cortex shows a consistent molecular architecture.
  • Males show more sex-biased gene expression. More genes differentially expressed (DEX) between the sexes were found in males than females, especially prenatally. Some genes found to have such sex-biased expression had previously been associated with disorders that affect males more than females, such as schizophrenia, Williams syndrome, and autism.
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    Our brains are all made of the same stuff. Despite individual and ethnic genetic diversity, our prefrontal cortex shows a consistent molecular architecture. 
Tero Toivanen

New Study: Autism has Multiple Genetic Roots | Suite101 - 3 views

  • The study’s major finding was that children with ASD have significantly more CNVs affecting their genes than children without ASD. Children with ASD have 20 percent more CNVs in general, and 70 percent more CNVs impacting genes known to be associated with ASD or cognitive problems. Significantly, many of the genes that are affected control important functions such as cell proliferation and cell-to-cell communication.
  • Some of the newly discovered genetic variants are inherited, and are found in parents or siblings of children with them. Others, however, seem to have originated spontaneously in the affected child, and do not appear in other family members.
  • While these findings add significantly to the scientific understanding of the genetic and biological underpinnings of ASD, the immediate usefulness is limited. That’s because there are a very large number of CNVs, and each child shows a different pattern of genetic changes. Each of these changes is rare; no CNV showed up in more than one percent of the children studied.
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  • “This will lead to a paradigm shift in understanding the etiology of autism,” says Stephen Scherer, a senior scientist at The Hospital for Sick Children in Toronto, Canada. “Until now, most scientists thought individuals with autism shared common genes. We now think each person has his own rare variations.”
  • If significant CNVs show up, behavioral treatment can be started early. That has been shown to improve children’s outcomes significantly. “If we provide stimulation early, while the brain is still plastic, we can improve cognitive development, social interaction and communication,” says Geri Dawson, Chief Science Officer of Autism Speaks, the major sponsor of the research project.
  • What this new research suggests is that autism and ASD probably result from the interaction between many different genes and a child’s environment. Rather than search for one single cause and one “magic bullet,” researchers will try to find as many significant genetic variants as possible, link them to the biological functions and pathways they control, and then search for medications that can improve or normalize the functioning of damaged pathways.
Tero Toivanen

What Do New Genetic Findings Mean to Families with Autism? - 0 views

  • reply from lead researcher Hakon Hakonarson:
  • The variant we detected at the 5p14 locus (common variant) has been present for a long time in the genome (most likely since man moved out of Africa) and this region is highly conserved between species which means that it is regulating gene expression and gene function (the CHD10 gene being the most critical one).
  • We know that the association is strongest in those individual who have the greatest abnormalities in social skills/interactions and those that show least interest in interactions; we have not detected any other characteristics yet, but we keep working on it.
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  • Once we learn about this difference, we can then look for medications that block the consequences of the variant and once we make sure they are safe, we can then start testing these new medications in children who are at risk of developing autism, with the objective of preventing autism (i.e., avoid breakdown in connections between nerves and abnormality in brain connectivity).
  • Response: Yes, all of them could be tested in utero; we have identified 10 new variations (9 rare and 1 common) and we have replicated (and confired) four other once that were previously published (neurexin 1, contactin 4, 15q11 and 22q11). However, we do not have a yes or no answer as to whether the fetus will be autistic -- but if we are testing a fetus in an autistic family the value of the test is much higher.
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