A new study claims to show for the first time that autism begins in the womb, while another examines possible environmental influences on autism development.
The origins of autism have been passionately debated by many scientists and commentators. What is known about autism is that it is a physical condition, which is linked to abnormal biology and brain chemistry.
Genes seem to play an important part in the development of autism - identical twins, for instance, are much more likely to both have autism than non-identical siblings. But there has not been any clear consensus in medical opinion about what other contributing causes there may be.
Some things that have been suspected as being linked to autism - but which have not been proven - include diet, changes in the digestive tract, mercury poisoning, problems with the body processing vitamins and minerals, and vaccines.
A recent, large study in the journal PLoS Computational Biology suggests that environmental pollution could be a contributing factor to autism risk, but the study was unable to name any specific toxins that might be responsible.
That study assessed 100 million US health insurance claims to look at rates of autism on a county-by-county basis. It also used genital malformations in boys - micropenis, undescended testicles and cases where the urethral opening is on the underside of the penis - as indicators of environmental pollution.
The researchers found that for every 1% increase in genital birth defects in a county, the rate of autism there increased by nearly 300%.
"Both genes and environment are important," emphasizes the lead researcher, Andrey Rzhetsky, a professor of genetic medicine at the University of Chicago in Illinois.
Study finding an in-utero basis for autism is the first to do so
The other new study, published in the New England Journal of Medicine, analyzed the brain tissue of children with autism.
The researchers - from the University of California, San Diego School of Medicine and the Allen Institute for Brain Science in Seattle, WA - examined 25 genes in the postmortem brain tissue of children with and without autism. These genes included biomarkers for brain cells in different layers of the cortex, genes that have been linked to autism and several control genes.
Analyzing the brain tissue of deceased children who had autism breaks ground with previous research, which instead has used the brain tissue of adults with autism and attempted to extrapolate back to what might have occurred developmentally.
The team found that key genetic markers across multiple layers of brain cells were missing in the brains of autistic children.
The video below illustrates how the researchers came to their findings:
Genetic defects occurred in 'focal patches' of brain tissue
"Building a baby's brain during pregnancy involves creating a cortex that contains six layers," says researcher Eric Courchesne, PhD. He continues:
"We discovered focal patches of disrupted development of these cortical layers in the majority of children with autism. This defect indicates that the crucial early developmental step of creating six distinct layers with specific types of brain cells - something that begins in prenatal life - had been disrupted."
But equally as important as the evidence of developmental disruption in children with autism, the team believes, is that these defects appeared in "focal patches," particularly around the frontal and temporal cortex. This suggests that this defect does not apply equally to all areas of the brain and may explain why different functional systems are affected in people who have autism.
The researchers found that, in children with autism, the prenatal step of creating six distinct layers with specific types of brain cells had been disrupted.
"The fact that we were able to find these patches is remarkable, given that the cortex is roughly the size of the surface of a basketball, and we only examined pieces of tissue the size of a pencil eraser," says researcher Ed S. Lein, PhD, of the Allen Institute for Brain Science. "This suggests that these abnormalities are quite pervasive across the surface of the cortex."
"The finding that these defects occur in patches rather than across the entirety of cortex gives hope as well as insight about the nature of autism," adds Dr. Courchesne.
The discovery of the patch-like nature of the defects could also explain why some toddlers with autism show improved symptoms with early treatment. The researchers think this supports the theory that the brain may be able to rewire neural connections to avoid defects.
The team claim their findings therefore raise hope that further understanding of these patches could allow scientists an insight into how that rewiring occurs, opening doors to potential new treatments and therapies.