A new study has found that a group of infections that can pass from a mother to her baby could raise the risk of autism for the child.
The study, published Monday, looked at nearly 3.7 million people born in Sweden between 1987 and 2021 for a link between a particular group of infections and both educational and neurological developments.
Of those, 975 were diagnosed with a congenital TORCH infections, which stands for toxoplasmosis, other, rubella, cytomegalovirus and herpes simplex. Other includes syphilis, varicella, mumps, parvovirus and HIV.
The study authors note that these pathogens are grouped for their unusual ability to cross the placenta to infect the fetus.
“It has long been known that these infections can cause intellectual disability. However, the link to autism has been less clear in previous research, which has often been based on small patient groups,” Hugo Sjöqvist, PhD student and the study’s lead author, said in a Monday news release.
“This study is the largest to date in this field and is based on national register data covering almost the entire population of Sweden.”
In the news release, study co-author Reneé M. Gardner said it’s important to emphasize that it’s unusual for these infections to be transmitted from mother to child.
“They account for a very small proportion of all cases of autism in the population, but for those children who are actually affected, we see a clearly elevated risk of both autism and intellectual disability.”
The study determined that children with a TORCH infection at birth were about three times more likely to be diagnosed with autism and more than seven times more likely to be diagnosed with an intellectual disability, compared to children who did not have an infection. Children with a TORCH infection were also 30 times more likely to have a “severe to profound intellectual disability.”
The authors highlighted the limited effect of TORCH infections at a national level in Sweden, as they are rare in newborns. They connect babies affected by TORCH infections to about 1.2 per cent of all cases of severe intellectual disability, and less than 0.04 per cent of autism cases in Sweden.
However, they do predict about 20 per cent of newborns born with TORCH illnesses to later develop autism.
“TORCH infections have a very strong risk of autism,” Sjöqvist said.
“But since they are so rare, even though they had an almost 200 per cent increase (in diagnoses connected to TORCH infections)... it’s a very very small portion of all autism cases could actually be explained by the TORCH infections,” Sjöqvist said in a joint CTVNews.ca interview with Gardner on Tuesday.
He clarified that most autism cases are explained by genetics rather than any external factors.
As part of their study, the researchers compared kids with TORCH infections to their siblings who did not. The researchers reported finding similar results.
“In this case, we have this one unique environmental factor where we can say with some pretty strong evidence that these two are linked,” Gardner said in the interview.
She explained that previous research conclusions were often neutralized once the “genetic background” of an autistic person’s family was examined, given how powerful genetics are in determining if a person is autistic.
“Genetic factors make a major contribution to autism, but they are not the whole story. Our study provides strong evidence that some specific early-life environmental exposures — in this case, rare congenital TORCH infections — can also influence neurodevelopment,” Gardner told CTVNews.ca in a Wednesday email.
The study strengthened previous findings that external forces, not just genetics, can affect if a person will be autistic, even if the TORCH infections are only a small factor.
“Part of the original clinical description of the congenital TORCH infections included intellectual disabilities and problems with the children’s cognitive development, so that part was definitely well known,” Gardner said.
“But the autism part was surprising, I would say,” she added. ”Also, the fact that the associations were quite specific for autism and intellectual disability was also surprising.”
The researchers did not find clear links between TORCH infections and other conditions like attention-deficit/hyperactivity disorder and obsessive-compulsive disorder, also known as ADHD and OCD.
There were, however, links with academic performance, with children who have TORCH illnesses generally performing worse in school than their peers who don’t have an infection.
The researchers said their work demonstrates the importance of a comprehensive national vaccination program. They cited rubella as an example, which has been largely eradicated in Sweden thanks to vaccination efforts.
With files from CTV News’ Jordan Fleguel
