The scientific backstory begins, fittingly, with the flu. Decades ago, epidemiologists noticed that mothers who contracted influenza during the second or third trimesters of pregnancy reported a higher incidence of psychiatric and neurodevelopmental disorders in their children. At the time, the observation was little more than a statistical curiosity. But when researchers later gained access to archived maternal blood samples, a clearer picture emerged: the risk appeared to track not with the virus itself but with the mother’s immune response to it. Chief among the suspects was interleukin-6, or IL-6, a signaling protein that stokes inflammation as part of the body’s defense against pathogens. Elevated IL-6 in the maternal bloodstream, it turned out, was the common thread. That discovery allowed scientists to build reliable rodent models of the phenomenon, in which a pregnant animal’s immune system is activated without any actual infection, reproducing the elevated risk of neurodevelopmental disorders in offspring.

What those models had largely lacked, however, was an epigenetic account of the damage. Most prior characterization of maternal immune activation in rodents was behavioral or electrophysiological—describing how the animals moved, responded to stimuli, or fired neuronal signals—without explaining what had changed inside the cells to produce those deficits. That gap is precisely what the Salk team, led by co-corresponding authors Margarita Behrens and Joseph Ecker, set out to close. Epigenetics refers to the layer of chemical tags and structural modifications that sits atop the base genetic sequence and determines which genes are turned on or off in a given cell. Unlike the genome itself, which is fixed at conception, the epigenome is malleable, making it a plausible target for environmental insults such as the inflammatory storm of maternal illness. If prenatal infection reshapes the developing brain, the epigenome is where that reshaping should leave its fingerprints.

To capture those fingerprints, the researchers used the field’s standard model of maternal immune activation: an injection of viral mimetic Poly(I:C), a synthetic double-stranded RNA that tricks the immune system into believing it has encountered an influenza virus. The treatment produces the same IL-6-driven inflammatory response as a genuine viral infection without introducing a pathogen. Using this model—referred to in the study as PIC-MIA—the team tracked epigenetic and transcriptional changes in the frontal cortex of mouse offspring from mid-gestation through two weeks after birth, comparing animals from immune-activated pregnancies with those from healthy pregnancies. The frontal cortex was the logical hunting ground: it is the brain region most associated with higher cognitive functions, and its development spans the entire window of vulnerability examined in the study.

The scale of the differences was striking. Across the developing cortex, the researchers documented thousands of epigenetic and gene-expression differences between the two groups. But the changes were not distributed evenly across all cell types. They concentrated, with remarkable specificity, in deep-layer neurons—a population of cortical cells that project long-range connections to other brain regions and are known to be generated during precisely the developmental window when maternal immune activation strikes. These cells form the structural backbone of cortical circuitry, and disruptions to their maturation ripple outward into the wiring of the entire brain.

At the molecular level, the team found that methylation patterns—the placement of small chemical methyl groups on the DNA—were especially altered in genomic regions that govern deep-layer neuron identity. The most consequential changes clustered at the binding sites of Tbr1, a transcription factor that serves as a master regulator of the developing brain, directing immature cells along the path to becoming deep-layer cortical neurons. Here the researchers encountered a genuine surprise. In the offspring of immune-activated mothers, Tbr1 was actually more abundant, and its binding sites were more heavily methylated than normal. Yet the genomic regions that Tbr1 typically regulates were downregulated, not upregulated. The explanation, the data suggest, is that the excess methylation was physically blocking Tbr1 from doing its job. The cell had produced more of its master architect, but methyl groups were sealing off the blueprints that architect needed to read. Deep-layer neuron development, deprived of proper Tbr1 direction, proceeded abnormally.

The implications deepened when the team cross-referenced their findings with the SFARI Gene Database, the reference catalog of autism-associated genomic alterations maintained for the autism research community. Among the high-confidence entries in that database—the genes scientists are most certain are genuinely linked to autism spectrum disorder—roughly twenty-five percent were dysregulated in the Salk dataset. In other words, the epigenetic disruptions caused by maternal immune activation were not scattered randomly across the genome; they landed preferentially on genes already known to matter for autism. That convergence between an environmental risk factor and a genetic risk landscape is exactly the kind of mechanistic bridge the field has been searching for, suggesting a route by which prenatal illness and inherited vulnerability may converge on the same developmental programs.

To confirm that the molecular changes had functional consequences, the researchers performed electrophysiological recordings on deep-layer neurons after the animals were born. The recordings confirmed what the epigenomic data predicted: the maturation of these neurons was measurably impaired in offspring of PIC-MIA pregnancies. The electrical properties that define healthy, fully developed cortical neurons were disrupted, demonstrating that the altered methylation and gene expression translated into altered neuronal function—a defect in the brain’s hardware, not merely its chemical profile.

The findings also carry an important caveat about determinism, one the researchers are careful to emphasize. Maternal infection changes the odds of neurodevelopmental outcomes; it does not seal them. “Infection changes the odds of whether neurodevelopment is affected—not everyone who gets sick during pregnancy is going to definitively have a child with a neurodevelopmental disorder,” says Joseph Ecker, professor and Salk International Council Chair in Genetics at Salk and a Howard Hughes Medical Institute investigator. This framing matters both scientifically and for public communication. The study identifies a risk-modifying mechanism, not an inevitability, and understanding the mechanism opens the door to interventions that could shift those odds back in the child’s favor—whether through maternal therapeutics that dampen harmful inflammation or through fetal interventions that protect vulnerable developmental programs.

Much remains unknown. The researchers still do not know exactly when during brain development the epigenetic damage occurs, or which stretch of pregnancy represents the window of greatest vulnerability to severe illness. “We are closer now to understanding the consequences of maternal infection, but this is only just the beginning of the story,” Ecker says. Behrens, for her part, frames the work as the payoff of a decade of methodical groundwork. “It’s just the tip of the iceberg. We are distilling all these things that we have been doing for ten years—analyzing epigenomes for years and years to get to the point that we can ask these questions. Now we can approach questions with more detail. It’s going to be a lot of fun moving forward.” As single-cell epigenomic technologies continue to mature, the ability to ask where and when specific molecular events derail specific neuronal lineages will only sharpen, bringing the field closer to preventive strategies for a class of disorders that currently affects millions of families.

What makes the study resonate beyond the laboratory is its unifying logic. A mother’s feverish immune response, a chemical tag on DNA, a transcription factor locked out of its binding sites, a neuron that fails to mature, a brain whose circuitry carries the imprint into adulthood—these are not separate stories but a single causal chain, now traced end to end in a mammalian model. The work demonstrates the lasting impact of prenatal immune challenges on offspring health and adds a mechanistic foundation to a decades-old epidemiological observation. In doing so, it transforms a correlation once glimpsed in flu-season statistics into a testable, targetable biological pathway—one that may ultimately guide the development of maternal or fetal therapeutics designed to protect the developing brain from the collateral damage of the immune system’s own defense.

The international research consortium, led by the University of Hong Kong in collaboration with Aston University’s Professor Ian Chi-Kei Wong, analyzed data from an unprecedented cohort of over 700,000 mother-child pairs spanning more than two decades. Their research leveraged an innovative sibling-matched design to isolate the effects of paracetamol from confounding genetic and environmental variables. By comparing siblings from the same mother, where one sibling was exposed prenatally to paracetamol while the other was not, the study gained unparalleled precision in dissecting the true impact of the medication.

Paracetamol remains the most widely recommended analgesic and antipyretic for pregnant women worldwide due to its established safety profile and efficacy. However, public anxiety intensified following statements from US federal agencies implying a possible causal link between prenatal paracetamol use and increased risks for ASD or ADHD. Such assertions triggered a wave of scientific scrutiny and cautious reevaluation of analgesic protocols during gestation. Despite affirmations from global health authorities including the WHO regarding paracetamol’s safety, the evidence base had remained fragmented and inconclusive until this comprehensive investigation.

Researchers accessed and synthesized electronic medical records covering 708,020 mother-child pairs in Hong Kong between 2000 and 2023. Data encompassed detailed records of paracetamol exposure timing, dosage, and usage patterns throughout pregnancy trimesters, alongside longitudinal neurodevelopmental assessments of the children. The methodological rigor incorporated sibling-matched controls to minimize biases stemming from socio-economic, genetic predispositions, and familial environmental factors that often obscure causal inferences in epidemiological studies.

The results were unequivocal. The analysis revealed no statistically significant association between prenatal paracetamol exposure and elevated risks of ASD or ADHD in offspring. This absence of correlation persisted irrespective of how frequently or persistently the drug was used during pregnancy, as well as irrespective of whether exposure occurred during the first, second, or third trimester. These findings unequivocally contradict earlier concerns suggesting a dose-dependent or trimester-specific increased risk.

This study’s implications extend well beyond scientific circles, providing critical reassurance to millions of expectant mothers globally. Dr. Shan Luo, a research assistant professor involved in the study and a mother herself, emphasized the personal resonance of these findings. Having suffered herpes zoster during pregnancy, Dr. Luo refrained from using paracetamol due to prevailing apprehensions, underscoring how misinformation can impact health decisions and quality of life during critical periods. The study now empowers clinicians and patients alike to prioritize maternal comfort and safety without fear of adverse neurodevelopmental outcomes.

On a technical level, this research highlights the transformative power of big data analytics combined with innovative epidemiological study designs. Sibling-matched cohort analysis, a relatively novel approach in pharmacovigilance research, permits more accurate disentangling of mediator variables by controlling for latent genetic and shared environmental confounders. Utilizing Hong Kong’s extensive electronic medical records infrastructure enabled this granular, large-scale analysis with appropriate statistical models to ensure result validity and generalizability.

Professor Ian Wong, who holds the Regius Chair in Pharmacy at Aston University and is also a professor at the University of Hong Kong, underscored the pivotal role of interdisciplinary collaborations and international partnerships. By integrating pharmacological expertise with robust data science methodologies and clinical insights, the team addressed a globally urgent medication safety question with both speed and scientific rigor. The strategic alliance between Aston Pharmacy School and HKUMed’s Department of Pharmacology and Pharmacy serves as a model for future large-scale investigations in maternal and child health.

Importantly, the study calls attention to the nuanced communication required in public health messaging, especially concerning medication use in vulnerable populations. Erroneous or premature conclusions about drug risks can lead to suboptimal therapeutic decisions and unnecessary suffering. By furnishing definitive evidence on paracetamol’s safety during pregnancy, the research alleviates undue fears, reinforcing the notion that analgesic stewardship must be grounded in comprehensive data rather than anecdote or speculation.

Given the prominence of ASD and ADHD as key neurodevelopmental disorders impacting millions worldwide, elucidating environmental risk factors remains a top public health priority. This study’s methodical approach and robust data affirm that prenatal paracetamol does not contribute measurably to these conditions, thereby narrowing the focus onto other potential etiologies such as genetic susceptibilities, perinatal factors, and broader environmental exposures.

In conclusion, this seminal research provides a pivotal advance in our understanding of prenatal medication safety, rectifying misconceptions surrounding paracetamol use in pregnancy. It underscores that expectant mothers requiring analgesic interventions can do so with confidence, safeguarding both their well-being and that of their developing children. The publication offers a foundation for future pharmacoepidemiological studies utilizing sibling-matched designs to untangle complex drug safety questions impacting vulnerable populations.

For those interested in exploring the scientific details of this investigation, the full paper titled “Prenatal Acetaminophen (Paracetamol) Use and the Risk of Autism and/or Attention-Deficit/Hyperactivity Disorder Among Sibling-Matched Cohorts” is accessible via JAMA Internal Medicine.

Subject of Research: People
Article Title: Prenatal Acetaminophen (Paracetamol) Use and the Risk of Autism and/or Attention-Deficit/Hyperactivity Disorder Among Sibling-Matched Cohorts
News Publication Date: 29-Jun-2026
Web References: https://jamanetwork.com/journals/jamainternalmedicine/article-abstract/2850975
References: DOI: 10.1001/jamainternmed.2026.2215
Keywords: Pregnancy, Human reproduction, Paracetamol, Acetaminophen, Autism spectrum disorder, ADHD, Neurodevelopmental disorders, Pharmacology, Drug safety, Sibling-matched cohort, Pharmacoepidemiology, Pain management during pregnancy

The maternal immune system’s activation during pregnancy, often triggered by infections or inflammatory conditions, has long been postulated to increase the offspring’s vulnerability to neurodevelopmental disorders such as autism spectrum disorder (ASD), schizophrenia, and intellectual disabilities. However, the molecular underpinnings governing this linkage remained elusive until now. Zhu and team approached this scientific conundrum by analyzing how gestational immune activation could lead to changes in gene expression profiles within critical brain regions during both prenatal and postnatal developmental windows.

Central to their findings is the role of epigenetics—heritable changes in gene function that occur without altering the DNA sequence itself. In this context, epigenetic modifications, including DNA methylation and histone modifications, sculpt the brain’s developmental architecture by modulating synaptic plasticity, neuronal connectivity, and circuit formation. The research highlights that immune activation disrupts these epigenetic marks, thereby altering the expression of genes essential for proper synaptic development and neurogenesis.

The investigators employed a multifaceted experimental framework encompassing animal models, high-resolution molecular profiling, and behavioral analyses to trace the cascade of molecular events initiated by immune activation. By examining maternal immune challenges at specific gestational stages, they identified temporal windows during which the fetal brain exhibits heightened sensitivity to epigenetic disruption. This temporal specificity underscores the complexity of in utero environmental influences on long-term cognitive and behavioral outcomes.

Their data demonstrate that gestational immune activation leads to aberrant epigenetic landscapes in the hippocampus and prefrontal cortex—regions integral to memory, learning, and executive functions. Altered methylation patterns observed in synaptic genes correlated with dysfunctional synaptic transmission and impaired neural network synchronization postpartum. These molecular signatures were consistently linked to behavioral phenotypes resembling neurodevelopmental disorders, bridging the gap between biochemical changes and functional consequences.

Importantly, this study also distinguishes between prenatal and postnatal effects, revealing that epigenetic reprogramming induced by maternal immune activation persists well beyond birth and impacts synaptic maturation during critical postnatal developmental phases. This discovery challenges previous notions that prenatal insults are transient and highlights the enduring nature of immune-mediated epigenetic modifications on neural circuitry formation.

Moreover, Zhu and colleagues elucidate how immune signaling molecules—including cytokines and chemokines—serve as mediators that trigger epigenetic alterations in neural progenitor cells and mature neurons. These pathways orchestrate complex feedback loops that influence chromatin structure and transcriptional activity, ultimately determining neuronal fate decisions and synaptic functionality. By pinpointing these molecular actors, the research opens avenues for targeted interventions aimed at mitigating immune-induced neurodevelopmental impairments.

The clinical implications of this research are vast. Understanding how gestational immune activation drives epigenetic dysregulation offers potential biomarkers for early diagnosis and risk stratification in at-risk pregnancies. It also fuels the pursuit of novel epigenetic therapeutics and anti-inflammatory agents capable of restoring normal developmental trajectories. Tailoring such interventions during identified critical developmental windows could revolutionize preventive and therapeutic strategies for a spectrum of neuropsychiatric disorders.

Another compelling aspect of the study lies in its exploration of environmental and genetic interactions. The team examined how genetic susceptibility intersects with immune-induced epigenetic changes, revealing that individuals harboring risk alleles experience amplified neurodevelopmental impairments following gestational immune challenges. This gene-environment interplay underscores the necessity of personalized medicine approaches in managing offspring neurodevelopmental health.

Methodologically, the research integrates cutting-edge epigenomic technologies such as bisulfite sequencing and chromatin immunoprecipitation sequencing (ChIP-seq) to map epigenetic alterations with exquisite precision. These tools facilitated the identification of specific loci undergoing differential methylation and histone modification following gestational immune activation. The rigorous analytical framework strengthens the validity and reproducibility of the findings, solidifying their impact on the neuroscience field.

To complement molecular data, the study incorporated advanced imaging techniques and electrophysiological recordings to assess synaptic integrity and neural network dynamics. These multimodal approaches confirmed that epigenetic perturbations engender quantifiable deficits in synaptic transmission efficiency and plasticity, phenomena critical for cognitive function. The convergence of molecular and functional evidence adds profound depth to the understanding of neurodevelopmental pathophysiology in the context of maternal immune activation.

As public health concerns about prenatal infection and maternal immune health grow, this research arrives at a critical juncture. It stresses the urgency of monitoring maternal immune status during pregnancy and lays the groundwork for clinical protocols that could mitigate neurodevelopmental risks via immunomodulatory treatments. These findings could influence obstetric practices worldwide, emphasizing immune health as a corner-stone of prenatal care.

Ultimately, Zhu, Li, and colleagues have crafted a seminal contribution to neurodevelopmental science, detailing how environmental pressures, such as maternal immune activation, reshape the epigenetic landscape to influence lifelong brain function. Their work not only elucidates fundamental biological principles but also charts a promising course for translational applications aimed at alleviating the burden of neurodevelopmental disorders.

This integrative study exemplifies the power of interdisciplinary research bridging immunology, epigenetics, and neuroscience. As the authors continue to unravel the complexities underlying gestational immune effects, future work may examine potential reversibility of epigenetic changes and assess novel therapeutic compounds. Such endeavors will be vital for translating these discoveries into real-world interventions.

In the coming years, this line of investigation is poised to transform how we understand and manage brain development in the context of prenatal environmental influences. Zhu et al.’s findings act as a clarion call to the scientific community, reminding us of the delicate molecular choreography that shapes our brains and the profound consequences when this choreography is disrupted by immune challenges during gestation.

Subject of Research: Effects of gestational immune activation on neurodevelopment and synaptic pathways via epigenetic mechanisms.

Article Title: Prenatal and postnatal effects of gestational immune activation on synaptic and neurodevelopmental pathways via epigenetic mechanisms.

Article References:
Zhu, B., Li, G., Saunders, J.M. et al. Prenatal and postnatal effects of gestational immune activation on synaptic and neurodevelopmental pathways via epigenetic mechanisms. Transl Psychiatry (2026). https://doi.org/10.1038/s41398-026-03884-z

Image Credits: AI Generated

DOI: https://doi.org/10.1038/s41398-026-03884-z