Researchers find activation of maternal immune system during pregnancy disrupts expression of key genes and processes associated with autism and prenatal brain development.
?For some infections, such as Zika, the virus passes through the placenta and directly attacks the fetus. For others, such as the H1N1 influenza, the virus induces maternal immune activation (MIA) by triggering a woman’s immune system during pregnancy. Both Zika and MIA mechanisms may lead to potentially disastrous neurological repercussions for the unborn child, such as microcephaly in the case of Zika or cortical abnormalities with excess numbers of neurons, patches of disorganized cortex, synapse mal–development and early brain overgrowth in some cases of MIA.

Large population–based studies suggest MIA caused by infection during pregnancy are also associated with small increases in risk for psychiatric disorders, including autism spectrum disorder (ASD). In a new study published in the journal Molecular Psychiatry, researchers at the University of California San Diego School of Medicine, University of Cyprus and Stanford University map the complex biological cascade caused by MIA: the expression of multiple genes involved in autism are turned up or down by MIA, affecting key aspects of prenatal brain development that may increase risk for atypical development later in life. “We provide novel evidence that supports the link between prenatal infections and biology known to be important in the development of autism,” said senior author Tiziano Pramparo, PhD, associate research scientist at the Autism Center of Excellence at UC San Diego School of Medicine. “There are different routes of importance. We highlight a specific pathway that seems to be key in driving downstream early abnormal brain development.”

“Our work adds to growing evidence that prenatal development is an important window for understanding key biology of relevance to neurodevelopmental conditions like autism,” added lead author Michael Lombardo, PhD, at the University of Cyprus. “MIA is an environmental route of influence on fundamental biological processes important for brain development. The influence it exerts overlaps with key processes known to be important in how the brain in autism develops.”

Pramparo said the effects are not caused by the infectious agents themselves. For example, increased levels of maternal cytokines may directly or indirectly alter gene expression in the fetus’ brain.

“These up– and down–regulated genes may lead to an excess or reduction in the normal amounts of proteins required for normal brain development,” Pramparo said. “Importantly, we have found that MIA–induced effects involve both single genes and pathways essential for early fetal neurodevelopment.” Among the large number of genes whose activity is altered by the maternal immune response, are a few that, when mutated, are thought to cause more genetic forms of autism in a small subset of all ASD toddlers.

Pramparo suggested the findings have multiple clinical implications.

“In general, the more we know and understand about a disrupted mechanism, the higher the chance of finding amenable targets for potential therapeutic intervention or for informing how to prevent such risk from occurring in the first place.”

Another implication, he said, is the potential to define the effects and clinical phenotypes based upon the underlying mechanisms: genetic, environmental or both.