Using stem cells, scientists have engineered neurons that provide the first human cellular model in which to study the development of autism.

The stem cells came from adult patients with Rett syndrome, a severe developmental disorder similar to autism.

Researchers sought to make neurons from these cells because "if we can understand the extreme case, we can understand all the others," said study researcher Alysson R. Muotri, assistant professor of pediatrics at the University of California, San Diego.

Now, researchers can use the cell model to test drugs and therapies to study how they can impact autism , Muotri said.

Often, it's hard to test autism treatments in animals because it's difficult to see the physical manifestations of the disorder researchers can't observe the impaired social interactions and communication that are the hallmarks of the disease in humans, Muotri said. Until now, the only other solution was drug testing directly in humans.

"Now, we're proposing that, before going to humans, we test in cells," he said.

To create the cells, researchers from the university and the Salk Institute for Biological Studies in California took cells from patients with Rett syndrome, and transformed them into cells similar to embryonic stem cells, called induced pluripotent stem cells.

In laboratory dishes, researchers turned the stem cells into neurons, which are signaling cells that make up the core of the nervous system.

But these neurons showed some abnormalities compared to neurons from healthy people, researchers found. They were smaller than healthy neurons, had fewer synapses for signaling other neurons and showed other signs of communication failure all signs of Rett syndrome.

When the cells were treated with drugs that corrected autism symptoms in mice, the abnormalities in the neurons were reversed.

"We don't know that the drugs that we used there can really work [in humans], but at least there's a proof of principle that the neurons are not locked in this state forever," Muotri said.

Because children don't often develop Rett syndrome until they are 6 to 18 months old, the finding suggests there may be a window of opportunity before the disease develops , for early diagnosis and preventive therapies, he said.

Researchers are now looking for more specific drugs that can target the neurons of people with autism. Muotri and his colleagues are now working to derive stem cells from children with sporadic autism , which is autism found only in children but not in their parents.

The study will be published tomorrow (Nov. 12) in the journal Cell.