Autism: ‘Serious’ risk factor in children that may predict a future diagnosis – new study

Autism is characterised by difficulties in socialising says doctor

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While researchers have found plenty of gene variants that appear to increase the risk of an autism diagnosis, it is still not clear why some people carrying these mutations develop autism spectrum disorders and some do not.

Some of the signs and symptoms of autism in adults include:

• Finding it hard to understand what others are thinking or feeling
• Getting very anxious about social situations
• Finding it hard to make friends or preferring to be on your own
• Seeming blunt, rude or not interested in others without meaning to
• Finding it hard to say how you feel
• Taking things very literally – for example, you may not understand sarcasm
• Having the same routine every day and getting very anxious if it changes.

In a study published in Science Advances, researchers point to a potential answer to the mystery of mutations developing into autism: severe infections during early childhood.

After an early immune challenge, male mice with a mutated copy of the tuberous sclerosis complex gene developed deficits in social behaviour linked to changes in microglia, the immune cells of the brain.

An analysis of the hospital records of more than three million children showed that children, particularly boys, who were hospitalised for infections between ages 18 months and four years, were more likely than those who were healthy to receive a future ASD diagnosis.

“We have genetic models, and we have a lot of in utero exposure models and early life stress models, but it’s pretty rare that people are blending the two to find that gene [and] environment interaction,” says Audrey Brumback, a paediatric neurologist at the University of Texas at Austin Dell Medical School.

“We knew that mutations predispose [people] for autism, but if you look in patients with genetic mutations, not everyone with that mutation has autism, and the question is why?” said neuroscientist Alcino Silva of University of California, Los Angeles (UCLA).

One such type of mutation, linked to autism in about half of the people who carry the variants, are in the tuberous sclerosis (Tsc2) complex one or two genes and can have a range of symptoms in addition to autism.

Mice with a mutation in Tsc2 have some of the same symptoms, but until about a decade ago, the social deficits that can show up in people with the mutations had not been recreated in the mouse model.

In 2010, Silva’s group showed that challenging the immune systems of pregnant mice caused ASD-like behaviour in their Tsc2 mutant offspring.

In the new study, the researchers further explored the interactions of genetics and environment, this time at later stages of development.

They injected either an immune stimulant or saline into wild mice and after the mice reached adulthood, the researchers tested their social behaviours with numerous social interaction tests and found that the social memory of the mice that had an infection was impaired.

“It was interesting that these deficits were unique to social memory and did not result in impaired sociability – one of the key hallmark tasks used to assess social interactions in mouse models of ASD,” Annie Ciernia, a neuroscientist at the University of British Columbia said.

“This suggests that postnatal viral infections could be disrupting unique neural circuits important for social memory that are vulnerable during early postnatal development,” Ciernia continued.

“This paper has to be [understood] as proof that you need to vaccinate your kids, since infectious diseases can not only be fatal, but can also raise the risk of ASD among children who survive”, says co-author Manuel López Aranda, a neuroscientist at UCLA.

The combination of basic science and the clinically relevant data analysis of more than three million children is “a slam dunk,” said Tanjala Gipson, a paediatric neurologist at Le Bonheur Children’s Hospital.

The researcher also emphasised that these preliminary findings are in mice and whilst there is a strong chance, the science may not necessarily translate to humans.

Therefore, Gipson explained that the next step would be determining whether there are biomarkers that indicate when children are more at risk.

Rapamycin, the drug the authors used to ameliorate the effects of simulated infection on the mice, is already being studied for tuberous sclerosis, the genetic disorder caused by Tsc1 and Tsc2 mutations, she noted. “It’s another reason for hope, and there’s always room for hope.”

Beyond that, the researchers hope to explore how and why autism can be different in women and men. For example, autistic women may be quieter, may hide their feelings and may appear to cope better with social situations. 

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