Brain inflammation is a hallmark symptom of autism, a new study reveals. Autism can be brought about by the actions of several genetic traits.

Autopsies were performed on corpses of people who had experienced autism during their lives, as well as subjects without the disorder. In all, 72 autistic and healthy brains were examined by researchers, from 104 samples.

Autism spectrum disorder (ASD) results in repetitive behaviors in subjects, and affects personal interactions with other people. Roughly one in 68 American children suffer from ASD. The disorder is five times more common among boys than girls.

Causes of autism are still a matter of question for medical researchers, although numerous factors appear to be able to trigger the disorder.

"There are many different ways of getting autism, but we found that they all have the same downstream effect. What we don't know is whether this immune response is making things better in the short term and worse in the long term," Dan Arking from the McKusick-Nathans Institute for Genetic Medicine at the Johns Hopkins University School of Medicine said.

Gene expression - the action of genetic codes bringing about health problems - was not studied in relation to autism, until now. One of the challenges facing researchers was that gene expression testing can only be performed on samples of brain tissue, not available until after death. This new study is  the most extensive survey ever performed of gene expression in brains of autistic individuals.

Abnormalities in brain and spinal cord cells had been detected in autistic subjects in previous studies. Arking and his team were able to identify microglial cells - a type of support cell that tracks down pathogens in the brain - as potentially central to the development of autism. The structures appeared to be constantly "turned on" in autistic patients, directing brain tissue to inflame, in order to fight an infection that is not present.

"This type of inflammation is not well understood, but it highlights the lack of current understanding about how innate immunity controls neural circuits," Andrew West, associate professor of neurology at the University of Alabama at Birmingham, told the press.

Researchers believe inflammation in brain tissue is not the root cause of autism, but is likely due to even more primary causes. However, it is possible that treatments to reduce inflammation could also alleviate symptoms of autism. Future research will explore this possibility, potentially leading to new treatments for the disorder.

Autism and its relationship to brain inflammation was detailed in the journal Nature Communications.