The actions of genes in the human brain are significantly different for people suffering from autism spectrum disorder (ASD), affecting factors such as nerve cell function and communication, immunity, and inflammation response, according to a study published online in Nature on May 25.
Led by Dr. Daniel Geschwind at the University of California, Los Angeles (UCLA), a group of scientists compared post-mortem brain tissue samples from 17 healthy individuals and 19 autism sufferers. They looked at gene expression in three areas of the brain associated with autism, and in the cerebral cortex, which is largely responsible for speech, emotions, creativity, and judgment.
"If you randomly pick 20 people with autism, the cause of each person's disease will be unique," said Geschwind in a press release. "Yet when we examined how genes and proteins interact in autistic people's brains, we saw well-defined shared patterns. This common thread could hold the key to pinpointing the disorder's origins."
The team found that more than 500 genes were expressed at different levels in the frontal and temporal lobes of the healthy brains, whereas there were hardly any expression differences in most of the ASD brains.
"In a healthy brain, hundreds of genes behave differently from region to region, and the frontal and temporal lobes are easy to tell apart," Geschwind said. "We didn't see this in the autistic brain. Instead, the frontal lobe closely resembles the temporal lobe. Most of the features that normally distinguish the two regions had disappeared."
The temporal lobes process and interpret sounds, and regulate hearing and language.
Two other patterns were observed that are associated with the disease: genes involved with nerve cell function and communication are less active, while those associated with immunity and inflammation are more active.
"Several of the genes that cropped up in these shared patterns were previously linked to autism," Geschwind said. "By demonstrating that this pathology is passed from the genes to the RNA [ribonucleic acid] to the cellular proteins, we provide evidence that the common molecular changes in neuron function and communication are a cause, not an effect, of the disease."
The scientists will continue their research on how gene expression is linked with autism in other parts of the brain.