A comprehensive new study conducted by researchers at the Karolinska Institutet has identified a significant association between rare, maternally transmitted infections during pregnancy and an increased risk of neurodevelopmental disorders in childhood. The findings, published in the prestigious journal JAMA Pediatrics, shed new light on the long-term impact of congenital infections—specifically those classified as TORCH pathogens—on brain development, autism spectrum disorder (ASD), and intellectual disability.
The study, which leveraged data from 3.7 million individuals born in Sweden over a 34-year period, provides the most robust evidence to date regarding the neurological consequences of these infections. While the researchers emphasize that such infections remain rare and represent only a small fraction of total cases of autism in the general population, the data reveals a stark increase in risk for the specific children who are affected.
Understanding the TORCH Group
The research focused specifically on a group of pathogens known collectively by the acronym TORCH. This group includes cytomegalovirus (CMV), rubella, toxoplasma, and various forms of the herpesvirus, among others. In a typical pregnancy, the placenta acts as a highly effective barrier, protecting the developing fetus from the vast majority of maternal infections. However, the pathogens within the TORCH category possess the unique and dangerous ability to cross the placental barrier, potentially causing a congenital infection that can directly impact the fetus during its most critical stages of development.
"It is important to emphasize that it is unusual for these infections to be transmitted from mother to child," explains Renée Gardner, a researcher at the Department of Global Public Health at the Karolinska Institutet and a contributor to the study. "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."
A Massive Longitudinal Analysis
To reach these conclusions, the research team conducted a massive longitudinal study, examining health and education records for 3.7 million people born in Sweden between 1987 and 2021. Within this vast demographic, the team identified 975 individuals who had received a formal diagnosis of a congenital TORCH infection. By following these participants for up to three decades, the researchers were able to track long-term health outcomes, including neurodevelopmental diagnoses and subsequent educational attainment.
The results were striking. Children who had been diagnosed with a congenital TORCH infection were approximately three times more likely to be diagnosed with autism later in life compared to their peers who had not been exposed to these infections. Even more pronounced was the correlation with intellectual disability, where the likelihood of a diagnosis was more than seven times higher.
Perhaps most concerning was the data regarding the severity of these disabilities. For children categorized with severe to profound intellectual disability, the disparity was even more dramatic, with the risk rising as much as 30-fold compared to the unexposed population.
Balancing Relative Risk and Population Impact
While the study highlights a dramatic increase in risk at the individual level, the researchers were careful to provide context regarding the overall public health impact. Because congenital TORCH infections remain relatively uncommon, they account for a very small percentage of the total burden of neurodevelopmental disorders across the population.
The researchers estimate that congenital TORCH infections are associated with approximately 1.2 percent of all severe intellectual disability cases in Sweden. When looking at autism, the percentage is even lower, with an estimated 0.034 percent of all autism cases in the country attributable to these specific infections.
However, when shifting the focus from the population level to the individual level, the findings are significant for families affected by these conditions. The research team estimates that roughly one in five children born with a congenital TORCH infection may go on to develop autism, a figure that underscores the profound nature of these prenatal events.
"It has long been known that these infections can cause intellectual disability," says Hugo Sjöqvist, a PhD student and the study’s lead author. "However, the link to autism has been less clear in previous research, which has often been based on small patient groups. This study is the largest to date in this field and is based on national register data covering almost the entire population of Sweden."
Investigating Family Factors and Educational Outcomes
One of the methodological strengths of the study was the use of sibling comparisons to ensure that the findings were not simply a byproduct of shared family characteristics, such as genetics or environmental upbringing. By comparing children who had experienced a TORCH infection with their own siblings who had not, the researchers were able to control for these confounding variables. The persistence of the association within these sibling pairs strongly suggests that the infections themselves, rather than inherited traits, are the primary driver of the increased neurodevelopmental risks.
Interestingly, the study did not find a similarly clear association between congenital TORCH infections and other neuropsychiatric conditions, such as ADHD or obsessive-compulsive disorder (OCD). This suggests that the impact of these infections may be somewhat specific to the domains of autism and general cognitive development.
Beyond clinical diagnoses, the researchers also observed measurable differences in academic performance. Even among children who did not meet the criteria for a diagnosis of autism or an intellectual disability, those with a history of congenital TORCH infection received, on average, lower grades in school than their peers. This finding suggests that these infections may cause more subtle, sub-clinical impacts on brain development that manifest as difficulties in educational settings.
Implications for Public Health and Prevention
The study’s findings reinforce the critical importance of prenatal care and the prevention of maternal infections. The researchers argue that while these congenital cases are rare, the long-term consequences for the affected individuals are significant, making prevention a vital public health objective.
"Our results suggest that certain infections transmitted to the fetus during pregnancy may have long-term effects on brain development," notes Gardner. "Although these congenital infections are rare, some of them can be prevented, which makes them important from a public health perspective."
The researchers point to the success of vaccination programs as a model for future efforts. The near-total eradication of rubella in Sweden following the introduction of national vaccination programs serves as a powerful example of how public health policy can effectively protect developing fetuses from devastating infections. Maintaining and strengthening these vaccination programs, alongside other preventive measures aimed at reducing the transmission of pathogens during pregnancy, remains a priority for pediatric and maternal health.
The research, which provides a clearer picture of the relationship between early-life infections and long-term neurodevelopment, highlights the necessity of continued vigilance in maternal healthcare. By understanding the mechanisms behind these risks, health professionals can better advocate for preventative strategies that shield future generations from these rare but impactful health challenges.
The project was supported by funding from the Swedish Research Council. As noted in the study’s disclosures, co-author David Mataix-Cols has received author’s fees from UpToDate Inc and is a partner in Scandinavian E-Health AB; however, it was stated that these affiliations are unrelated to the findings or the publication of this research.
