Scientists might have discovered a link between autism and serious childhood infections later in life.
The immune response was activated in young male mice, which later led to mice having difficulty recognizing familiar faces.
These findings are supported by a study that included more than 3.6 millions children who were hospitalized.
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Scientists are now closer to understanding autism and the best ways to treat it. This month's study suggests that men with a genetic predisposition to autism spectrum disorder may be more likely to receive a diagnosis due to severe childhood infections.
The study was done on mice by scientists at the University of California Los Angeles. It's too early to know what the implications for humans. Other research suggests a similar relationship: Researchers at the University of Chicago used data from the same study to find that autism-stricken boys were more likely to be hospitalized for infections between 1.5 and 4. This was in contrast with boys who weren't diagnosed. The UCLA study did not examine whether autism was caused by any specific virus. However, the UCLA dataset contained more than 3.6million children with various infections.
Alcino Silva, UCLA's Integrative Center for Learning and Memory director, stated that the similarities between mouse and human data are "so striking that it's highly unlikely they're unrelated".
Research supports the notion that autism can be caused by genetic factors. The environment, such as a viral infection plays a part.
A mouse study offers an explanation. Childhood infections could cause the body's immune system to express more genes coded for microglia. This can lead to brain development problems, which may be responsible for some of the autism-related traits, like difficulty communicating verbally and recognition of familiar faces.
Researchers experimented with drugs to target microglia and found that they did not cause the social problems in adult mice, but that they could have reversed them.
Mock-viral infections in male mice caused difficulty for them to recognize familiar faces
A laboratory mouse that was used in a preclinical research at the Novosibirsk Tuberculosis Research Institute, Russia on March 23, 2017. Kirill Kukhmar/TASS/Getty Images
Because scientists cannot ethically infect people with viruses, studies in mice can often be crucial to understanding how viruses affect human and animal health.
Researchers used mice born with tuberous sclerosis, a genetic disorder that is linked to autism in humans, for the UCLA study. Silva stated that only half of the people with this disorder go on to develop autism. Researchers were trying to find out why.
They started by injecting some mice with a chemical to stimulate the immune system, similar to a viral infection. The placebo was given to the rest of them.
Only the male mice who received the chemical at birth experienced impaired social behavior as adults, and only those mice were affected by it. These mice couldn't distinguish between a mouse that they had previously seen and one they hadn't.
Another UCLA lab replicated the study, and discovered that mice treated with the chemical had less skill in communicating with each other. This is a hallmark trait of autism.
Researchers concluded that early viral infections could be combined with genetic mutations to lead to autism diagnosis. However, this is only true for men.
Manuel Lpez Aranda, the study's principal author, said that the female appears to be less affected than their male counterparts. "Maybe this is because of the microglia."
Lpez-Aranda suggested that boys' and girls' microglia might be at different developmental stages in their youth, which could explain why autism is more common in men.
Scientists are closer to finding autism treatments
The UCLA study teaches us that viral infections are not to be underestimated.
Dr. Lopez-Aranda at the laboratory. Dr. Lopez-Aranda
Lpez-Aranda stated, "Something that must be clear from this research is: please vaccine your children." Our results and human data suggest that children who aren't vaccinated for polio will have a greater chance of developing autism spectrum disorder than those who are vaccinated.
Silva suggested that severe childhood infections could also be associated with a higher risk of developing psychiatric disorders such as schizophrenia, anxiety, and depression. This concept is being further explored by researchers.
The UCLA study has shown that rapamycin (a drug that is approved for rare lung diseases) prevented male mice's forgetting familiar faces, or reversed the memory loss after they had been diagnosed. This could indicate that children with severe viral infections may be able to receive treatment that helps prevent them from developing autism.
Silva stated that scientists are only at the beginning of their research.
He said, "We have some pieces of the puzzle but only two or three pieces of the 1,000-piece puzzle."
