The Autistic Neuron
published: Oct. 7, 2010, recorded: May 2009, views: 3136
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This self-described “basic neuroscientist” confesses he never thought he’d give a talk on autism, but as Mark Bear recounts, decades of research in the basics are now paying off with important insights into the etiology and treatment of brain disorders, including autism.
Bear provides a primer on this developmental disorder, noting that its roots are biological, it is highly heritable, and astonishingly prevalent: one in 150 people express some of the symptoms of autism. These fall on a spectrum, from severely reduced social behavior, abnormal language, repetitive movements, seizures and mental retardation, to the milder Asperger’s Syndrome, where individuals are often academically successful, but socially awkward. Particularly significant to Bear: Autism’s underlying genetic changes manifest themselves in problematic communication between neurons.
To unravel autism, researchers are examining its clinical heterogeneity, “genetic risk architecture,” and how it alters brain connections and function. One of the difficulties in approaching autism is that a variety of genetic mutations can result in autistic behaviors, and only a few of these mutations have been identified. Bear himself has been probing the single gene disorder, Fragile X syndrome (responsible for about 5% of the cases “of full-blown autism.”) In Fragile X, the FMR1 gene is silenced, leading to a missing protein that serves as a key regulator of brain proteins involved in neuron communication. Without FMR1, “the brakes are missing,” and there’s excessive protein synthesis leading to altered brain function.
Bear hypothesized that it might be possible to correct Fragile X by bringing the system back in balance. He created mice models of the disease, and found that by reducing the number of neurotransmitter receptors that respond to the excessive brain proteins, he could ameliorate or correct Fragile X defects. These receptors are “druggable targets,” and, says Bear, “if the treatment works in fly, fish or mouse, it better work in humans or Darwin was wrong.”
Based on this work, drug companies are devising compounds to test in human clinical trials of Fragile X syndrome. In addition, Bear notes, colleagues have discovered that other mutations connected with autism also involve protein regulation problems. “This gets us excited, because it looks like a common pathway that causes synaptic dysfunction in different diseases that may ultimately manifest as autism. If that’s the case, then treatment for the disorder may be efficacious in multiple disorders.”
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