The Link between Common and Rare Forms of Autism

synapseAccording to recent research, rare forms of autism share a molecular signature with more common versions of the disorder. This finding is particularly intriguing to medical researchers, as it leads them to believe that autism is linked to a single genetic defect, also found in more complex forms of the disorder.

Researchers at the 2014 Society for Neuroscience annual meeting stated that a rare form of autism is linked to a duplication of the 15q11-13 chromosomal region, which is also duplicated in more common forms of autism.  Approximately 1 in 12,000 children carry the duplication, with about 41 percent of these individuals having autism.

Daniel Geschwind, lead researcher, analyzed patterns of gene expression in postmortem brains for 16 adults with idiopathic autism, meaning there was an unknown cause, along with the brains of 8 with autism and 15q11-14 duplications. According to their findings, the brains of those with idiopathic autism express lower levels of genes that play a role at neuronal junctions, or synapses, compared with controls. They were intrigued to find that the brains of those with the duplications showed the same trend, only to a more severe extent.

Geschwind, a professor of neurology, psychiatry, and human genetics at the University of California, Los Angeles, states, “It’s kind of remarkable. This is showing that a single gene disorder has the same pattern [as idiopathic forms of autism].”

Last month, two large studies that sequenced exomes, the parts of a genome that encode proteins, discovered that 50 “high-confidence” autism candidate genes are involved in two critical processes, neuronal connectivity and the control of gene expression. Geschwind states, “The proof is the replication. Although autism is very heterogeneous, we can capitalize on these findings to identify common molecular pathways.”

Geschwind and his team believe that autism, in all its forms, may develop from inherited genetic defects, causing dysfunctional synapses. In an attempt to correct the dysfunction, the brain sets off an inflammatory response, resulting in fewer active synapses, creating an imbalance between excitatory and inhibitory signaling, common to all those on the autism spectrum.

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