Potential breakthrough as experts discover factor during pregnancy they think causes autism

Scientists have grappled with the puzzle of autism's origins for decades - now a study suggests a bad cold or flu during pregnancy could be a cause.

They've shown that when the mother's immune system is ramped up in response to a viral infection, it can stunt the development of the growing baby's brain.

Female embryos seemed protected from these effects, but one third of male embryos were impacted to some degree, according to the research on mice.

This aligns with the fact that autism is more prevalent in boys than girls, said the team from Cold Spring Harbor Laboratory (CSHL) in New York.

Researchers simulated a viral infection in mice and tracked the fetus' reaction to how the mom's immune system responded to a cold or flu virus, known as maternal immune activation (MIA).

MIA is activated when the immune system kicks into high gear, increasing the levels of cytokines and chemokines which can cross the placenta and baby's blood-brain barrier.

Chemokines fight the flu by moving other immune cells, like cytokines, to the site of the infection.

Cytokines are small immune cells that fight off harmful pathogens by summoning other immune cells, creating symptoms like fever, runny nose and body aches.

Because a fetus' brain is so sensitive to environmental signals in the womb, this reaction can cause a wide range of behavioral issues including social impairments like autism spectrum disorder.

Irene Sanchez Martin, a postdoctoral student at CSHL, said that her recent experiments with mice showed that when the mother contracted a virus, the embryo's brain development slowed.

'The difference in my work is that I check what happened to the fetus 24 hours after exposure to maternal inflammation, rather than analyzing the behaviors of the offspring as adults,' she said.

Sanchez Martin focused on how prenatal inflammation caused by the cold or flu impacted the developing fetus' brain.

Her work did not look at other factors that cause mothers' immune systems to go into overdrive, such as in response to a vaccine, being obese or having underlying conditions.

However, well-established global studies have shown that many vaccines actually offer protection against infant illnesses by passing antibodies through the mother to the fetus before it is born.

Flu vaccines work differently than the active illness because it forces the body to produce antibodies which prepares the autoimmune system so it doesn't cause inflammation and other symptoms.

Santhosh Girirajan, an associate professor at Pennsylvania State University who studies the genetic underpinnings of neurodevelopmental disorders told NBC News: 'We know for sure, for so many years now, that vaccines don't cause autism.'

Prenatal inflammation is thought to impact how the growing baby's brain organizes the neural networks which connect cells and synapses.

If these are disrupted, the number of neurons and synapses in the brain can decrease which has been connected to people developing autism. 

One of the most major breakthroughs from Sanchez Martin's study showed that although female embryos appeared to be protected from the MIA, about one-third of male embryos showed signs of a brain development deficit that was consistent with autism.

Data has shown that autism is more common in males than in females, with four in 100 boys and one in 100 girls having the disorder in the US. 

Additional research is still needed to unravel the connection between the immune system's reaction to a virus and how it impacts the fetus.

More than 5.4 million people in the US are currently diagnosed with autism and 40 to 80 percent are likely related to genetics, but that still means 20 to 60 percent are caused by other factors.

Diagnosing early is crucial in autism because there are currently no treatments, and it takes years to test and diagnose the disorder.

Sanchez Martin said her research is still in the early stages and more needs to be conducted to definitively link cold and flu viruses to autism. 

However, she is hopeful that future findings could help doctors recognize the early warning signs of autism before a child is born.

Autism among children is on the rise throughout the US, with the Centers for Disease Control and Prevention (CDC) reporting that in 2000 an estimated one in 150 eight-year-olds had autism.

But by 2020 that number had skyrocketed to one in 36 eight-year-olds.

The increase could be attributed to physicians getting better at identifying cases of autism and more awareness surrounding the disorder.