Gilles / Science Source
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This article is more than five years old. Autism research — and science in general — is constantly evolving, so older articles may contain information or theories that have been reevaluated since their original publication date.
A new candidate gene for autism, called synapsin 2 (SYN2), regulates chemical messenger release across the connections between neurons, reports a study published 4 September in Human Molecular Genetics1.
Neurons signal across their junctions, or synapses, using bubbles of membrane containing chemical messengers that drift across the gap from one neuron to another. A family of proteins called synapsins regulates this process. In particular, SYN2 helps place these bubbles, or vesicles, into position at the synapse, so they are ready for release when the neuron is activated.
Several proteins involved in regulating synaptic signaling are implicated in autism, prompting researchers to investigate synapsins’ role in the disorder. One study found mutations in SYN1 in people with autism or epilepsy. Mice lacking SYN2 have cognitive deficits and are less social than controls2. Common variants in SYN2 may also contribute to the risk of epilepsy3.
In the new study, researchers sequenced the SYN2 gene in 190 people who have autism, 143 people with epilepsy and 335 controls. Three people with autism, one person with epilepsy and no controls have a harmful mutation in SYN2, the study found.
Of the autism-linked SYN2 mutations, one prevents production of the protein entirely, whereas the other two alter only a single amino acid.
Interestingly, all three mutations are in men with autism and were inherited from unaffected mothers. This supports the theory that it may take more mutations to lead to autism in women than it does in men, the researchers say.
Mouse neurons lacking SYN2 have fewer vesicles ready to be recycled to the synapse. The mice also show delays in the generation of new neurons, and those neurons that do form have fewer branches.
Adding the gene for normal SYN2 to cultured mouse neurons lacking SYN2 fixes the deficits in vesicle recycling. None of the versions of the gene with an autism-linked mutation is able to do this, however. One of the mutated genes does resolve the problems with neuronal development, suggesting that the mutation is less severe than the other two.
References:
1: Corradi A. et al. Hum. Mol. Genet. Epub ahead of print (2013) PubMed
2: Dyck B.A. et al. Synapse 63, 662-672 (2009) PubMed
3: Cavalleri G.L. et al. Lancet Neurol. 6, 970-980 (2007) PubMed
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