Cells taken from people with a rare syndrome linked to autism could help explain the origins of the condition, scientists suggest.
The Stanford University team turned skin cells from people with "Timothy syndrome" into fully-fledged brain cells.
The abnormal activity found in these cells could be partially corrected using an experimental drug, Nature Medicine reports.
UK researchers warned the findings might not apply to everyone with autism.
Compared with the hundreds of thousands of people worldwide thought to show characteristics of autism, "Timothy syndrome" is vanishingly rare, affecting an estimated 20 people across the planet.
People who have the syndrome frequently display autistic behaviour, such as problems with social development and communication.
Because it is caused by a single gene defect rather than a combination of small genetic flaws, each making a tiny contribution, it presents a useful target for scientists looking to examine what goes wrong in the developing brain of a child with autism.
Ready for work
The US researchers used a technique developed recently to generate brain cells called neurons from only a sample of the patient's skin.
This allowed them to examine their development in the laboratory, and even use them to test out possible treatments.
They found obvious differences between neurons grown from Timothy syndrome patients, and those from healthy "control" subjects.
The healthy neurons developed into different subtypes, ready for work in different regions of the brain.
In contrast, the proportion of neurons developing into each subtype was different in the Timothy syndrome samples - more were equipped to work in the upper part of the cerebral cortex, and fewer in the lower part.
This meant there were fewer neurons equipped to work in a part of the brain called the corpus callosum, which has the role of helping the left and right "hemispheres" of the brain communicate.
These differences echoed those already observed in mice specially bred with the Timothy syndrome genetic fault.
In addition, the neurons were making too much of a particular body chemical linked to the manufacture of dopamine and norepinephrine, which play a significant role in sensory processing and social behaviour.
Dr Ricardo Dolmetsch, who led the study, said that the abnormalities found tallied with other evidence that autism was due in part to poor communication between different parts of the brain.
The team managed to reduce significantly the number of these malfunctioning neurons by adding a drug as they developed.
This, they said, meant it might be possible one day to treat this defect in a real patient, although the drug used was not currently suitable for children due to side-effects.
The National Autistic Society gave a cautious welcome to findings, but warned that they did not necessarily offer insights into every form of autism.
Researcher Georgina Gomez said: "Timothy syndrome is only one form of autism and so these findings only give a very limited picture of what might cause the condition.
"More work would need to be done to substantiate this particular piece of research."