From: Reuters
Published December 5, 2007 06:18 PM

Missing protein may underlie autism: U.S. study

By Julie Steenhuysen

CHICAGO (Reuters) - Autism and other brain disorders may be the result of a missing protein important for building communication networks in the brain, U.S. researchers said on Wednesday.

Researchers at the Massachusetts Institute of Technology found that an enzyme called Cdk5 that instructs a synapse-building protein called CASK may be going awry, causing a breakdown in the formation of synapses.

Synapses allow information from one neuron to pass to another and are essential for the ability to learn and remember.

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"If there is a reduction in the number of synapses, that is going to profoundly affect the function of the nervous system," said Li-Huei Tsai, an MIT professor and Howard Hughes Medical Institute researcher, whose study appears in the journal Neuron.

Cdk5 is a kinase, an enzyme that changes proteins. Its primary task is to help new neurons form and migrate to their correct positions during brain development. But Tsai's study suggests it may also play a role in the formation of synapses.

The research offers a possible explanation for the underlying molecular causes of autism, she said in a telephone interview.

Tsai and colleagues genetically modified mice to either lack Cdk5 entirely or to have a very active form of it. She and colleagues then removed some of the cells and analyzed their growth in a petri dish.

"We show that if Cdk5 fails to facilitate CASK, then there is a very profound defect in synapse formation," Tsai said.

It affects the formation of synapses, reducing the number formed and impairing their function, she said.

People with autism spectrum disorders suffer in varying degrees from limited social interactions, lack of verbal and non-verbal communication and other abilities.

As many as 1.5 million Americans have some form of autism, according to the Autism Society of America. The exact cause of autism is unknown.

"The most accepted hypothesis for autism is that there is a defect in synapse formation," Tsai said, adding that mutations of genes directly connected to CASK have already been identified as being associated with autism.

Mutations of CASK and Cdk5 are also identified in certain patients with mental retardation.

"I think this study strongly suggests this pathway involving Cdk5 ... is intimately involved (in autism)," she said.

(Editing by Philip Barbara)

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