Neuroscientists find that two rare autism-related disorders are caused by opposing malfunctions in the brain.
Most cases of autism are not caused by a single genetic mutation. However, several disorders with autism-like symptoms, including the rare Fragile X syndrome, can be traced to a specific mutation. Several years ago, MIT neuroscientist Mark Bear discovered that this mutation leads to overproduction of proteins found in brain synapses — the connections between neurons that allow them to communicate with each other. In a paper published today in Nature, Bear and colleagues have now shown that tuberous sclerosis, another rare disease characterized by autism and mental retardation, is caused by the opposite malfunction — too little synthesis of those synaptic proteins. Though the findings might seem counterintuitive, they fit into the theory that autism can be caused by a wide range of brain-synapse glitches, Bear says. “The general concept is that appropriate brain function occurs within a very narrow physiological range that is tightly maintained,” he says. “If you exceed that range in either direction, you have an impairment that can manifest as this constellation of symptoms, which very frequently go together — autism spectrum disorder, intellectual disability and epilepsy.” Furthermore, the study suggests that any potential drugs developed to treat the cellular origins of autism would need to be carefully matched to the patient to ensure they do more good than harm. Drugs developed to treat Fragile X syndrome have shown encouraging results in human studies and are currently in Phase III clinical trials.
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