The study, published in BMC Pediatrics, was led by a team at the Women and Children’s Medical Center of Shenzhen Maternity and Child Healthcare Hospital affiliated with Southern Medical University. The investigators started with an unusually complete dataset: 2,652 deaths of children under five years of age recorded in Shenzhen between January 2016 and December 2023. From this mortality cohort, they applied prespecified, record-based cause-of-death exclusions and removed deaths occurring within 72 hours of birth, reasoning that very early neonatal deaths typically involve distinct clinical circumstances and are less likely to reflect undiagnosed metabolic disease. That filtering left 1,982 children eligible for metabolic investigation.

The critical resource was the archived dried blood spots, the small cards of filter paper collected from nearly every newborn in China as part of routine screening programs. These spots preserve a biochemical snapshot of the infant’s blood in the first days of life. Dried blood spots were available for 652 of the eligible children, and the team analyzed each one for 43 metabolites using tandem mass spectrometry, a technique that can precisely quantify tiny amounts of amino acids, acylcarnitines, and other small molecules in a single rapid run. The screening panel was designed to flag 48 different conditions, using both individual metabolite concentrations and prespecified metabolite ratios, since ratios often discriminate true disease from benign variation more reliably than any single value.

Tandem mass spectrometry works by ionizing the compounds extracted from the blood spot and then sorting them by their mass-to-charge ratio in two sequential stages, which allows the instrument to distinguish closely related molecules such as the various acylcarnitines that accumulate when fatty acid oxidation is impaired. When a fatty acid oxidation enzyme is deficient, the body cannot efficiently break down fats for energy, and specific intermediate acylcarnitines build up in the blood in characteristic patterns. Elevated concentrations of these markers, or abnormal ratios between them, serve as biochemical fingerprints of the underlying enzymatic block. In this cohort, 50 of the 652 tested children were flagged as positive by the MS/MS panel, a striking yield given that none of them had received a metabolic diagnosis before death.

To determine whether these biochemical signals reflected genuine disease, the researchers turned to whole-exome sequencing, a next-generation sequencing approach that reads the protein-coding regions of all roughly 20,000 human genes. Because most known inborn errors of metabolism are caused by variants in genes encoding enzymes, transporters, or cofactor proteins, the exome captures the great majority of the relevant disease space. The team sequenced all 50 MS/MS-positive cases and interpreted the variants according to American College of Medical Genetics and Genomics and Association for Molecular Pathology criteria, the standard framework for classifying sequence variants as pathogenic, benign, or uncertain.

The molecular work delivered definitive answers in 13 of the 50 cases, or 26 percent. Twelve of these were inborn errors of metabolism, and one child turned out to have Smith-Magenis syndrome, a genomic disorder caused by a deletion on chromosome 17 that is not a metabolic disease at all but which had produced a misleading biochemical signal. One additional case was classified as probable ornithine transcarbamylase deficiency, a urea cycle disorder that can cause lethal hyperammonemia but which often eludes both standard screening and postmortem testing. Among the definitively diagnosed metabolic cases, the spectrum included fatty acid oxidation disorders, which emerged as the dominant category, consistent with the known tendency of these conditions to present as sudden, catastrophic illness in a previously healthy child, sometimes triggered by fasting or infection.

The diagnostic categories named in the study’s abbreviations read like a catalogue of rare but devastating pediatric disease: very-long-chain acyl-CoA dehydrogenase deficiency, carnitine-acylcarnitine translocase deficiency, systemic primary carnitine deficiency, multiple acyl-CoA dehydrogenation deficiency, methylmalonic acidemia, pyruvate dehydrogenase deficiency, ethylmalonic encephalopathy, and mucolipidosis II or III alpha/beta. Each of these conditions has a distinct biochemical signature and a distinct genetic cause, and each is potentially detectable, and in some cases treatable, if identified in time. The fact that they surfaced only after death underscores the central argument of the paper: expanded newborn screening is not universally implemented, and where it is absent or incomplete, lethal metabolic disease can pass through the health system entirely unrecognized.

One of the most clinically informative findings emerged from the comparison between the 13 definitively diagnosed cases and the 37 MS/MS-positive cases that lacked a definitive molecular diagnosis. The diagnosed children had significantly lower rates of low birth weight, 31 percent versus 84 percent; preterm birth, 15 percent versus 78 percent; and obstetric complications, 46 percent versus 78 percent, with P values below 0.001 for the first two comparisons and 0.040 for the third. In other words, the children whose deaths were ultimately explained by inherited metabolic disease were far more likely to have been born at term with normal birth weight and uncomplicated pregnancies. This pattern suggests that a metabolic cause of death should rise higher on the differential diagnosis when a seemingly healthy, full-term baby deteriorates or dies without an alternative explanation, whereas MS/MS abnormalities in preterm or low-birth-weight infants may more often reflect the physiological turbulence of prematurity rather than true inherited disease.

The study also examined how well the biochemical and genetic evidence agreed with each other, a question of real practical importance because discordant findings complicate diagnosis and family counseling. Among the 13 definitively diagnosed cases, clear metabolite-genotype concordance was observed in nine, or 69.2 percent, meaning the biochemical pattern and the pathogenic variants pointed to the same disease. Partial concordance was seen in two cases and non-concordance in two. These discordant cases illustrate a well-known limitation of newborn screening panels: metabolite levels can be influenced by age, feeding, liver function, and prematurity, and a positive screen is not a diagnosis. The authors argue that this is precisely where sequencing adds decisive value, establishing molecular diagnoses and clarifying atypical, nonspecific, or biochemically confusing findings that MS/MS alone cannot resolve.

The implications reach well beyond Shenzhen. The study provides direct evidence that retrospective analysis of archived dried blood spots can convert unexplained pediatric deaths into explained ones, offering families a diagnosis, clarifying recurrence risk for future pregnancies, and identifying relatives who may carry the same condition. Just as importantly, it strengthens the case for broader access to expanded MS/MS newborn screening worldwide, since every undiagnosed case in this cohort represents a child whose condition was, in principle, detectable at birth. The authors advocate a risk-stratified approach to genomic testing, reserving whole-exome sequencing for cases that remain clinically or biochemically unresolved after screening. As sequencing costs continue to fall and blood spot archives grow, the combination of metabolomics and genomics may become a standard tool not only for diagnosing living children but for understanding why some of the most vulnerable never survive their first years.

Subject of Research: Detection of undiagnosed inborn errors of metabolism in unexplained early childhood deaths using newborn dried blood spot screening and whole-exome sequencing

Article Title: Inborn errors of metabolism in unexplained early childhood deaths: a retrospective cohort study combining MS/MS and WES

Article References: Zhou, L., Yang, X., Wu, D., Zhang, L., Tu, X., Zhan, Z., Xie, S., Xu, Y., Liu, C., Wu, B., & Liu, W. (2026). Inborn errors of metabolism in unexplained early childhood deaths: a retrospective cohort study combining MS/MS and WES. BMC Pediatrics. https://doi.org/10.1186/s12887-026-07740-3

Image Credits: AI Generated

DOI: 10.1186/s12887-026-07740-3

Keywords: inborn errors of metabolism, newborn screening, tandem mass spectrometry, whole-exome sequencing, dried blood spots, early childhood mortality, fatty acid oxidation disorders, pediatrics, metabolomics, genetic diagnosis, urea cycle disorders, Shenzhen

The research team, led by investigators at Karolinska Institutet, linked six national health and socioeconomic registers covering every live-born singleton in Sweden across a fourteen-year window. Of the 1,455,645 children included, 90,046, or 6.2 percent, were born to mothers diagnosed with an autoimmune disease before or during pregnancy. These conditions, which range from type 1 diabetes and autoimmune thyroiditis to rheumatoid arthritis, lupus and inflammatory bowel disease, arise when the immune system mistakenly attacks the body’s own tissues, sustaining chronic inflammation and producing autoantibodies that can cross the placenta.

Over a median follow-up of 15.3 years, yielding more than 22 million person-years of observation, 426 deaths occurred among children of mothers with autoimmune diseases compared with 5,728 deaths among the unexposed. After adjusting for birth year, maternal age, education, country of birth, parity, marital status, smoking in early pregnancy and pre-existing maternal cardiovascular disease and type 2 diabetes, children of exposed mothers had a 22 percent higher risk of death from any cause, corresponding to a hazard ratio of 1.22. The estimate proved stable across successive statistical models, suggesting that observable socioeconomic and health differences between the groups could not account for the association.

Beneath the overall figure lay striking heterogeneity. Maternal type 1 diabetes roughly doubled offspring mortality risk, with a hazard ratio of 1.99, and elevated risks also appeared for connective tissue diseases and autoimmune thyroiditis. In contrast, maternal skin, blood and gastrointestinal autoimmune conditions showed little or no association. The endocrine diseases carry particular biological weight because they combine immune dysregulation with metabolic disturbance, a combination known to impair placental function and fetal growth, and the study’s authors note that the type 1 diabetes findings align with earlier smaller studies that reported lasting consequences for children exposed to hyperglycemia in utero.

Perhaps the most consequential discovery concerned timing. When follow-up was divided by age, the association was strongest during infancy, with a hazard ratio of 1.21 in the first year of life, while estimates for childhood, adolescence and young adulthood were weaker and statistically imprecise. Cause-of-death analysis reinforced this developmental picture: the excess risk was driven overwhelmingly by natural causes, specifically conditions originating in the perinatal period, with a hazard ratio of 1.43, and congenital malformations and chromosomal abnormalities, at 1.29. There was no clear association with infections, cancers, circulatory or nervous system diseases, and no association whatsoever with unnatural deaths such as accidents, an outcome-based negative control that strengthens confidence in the specificity of the biological signal.

Determining whether maternal disease itself causes harm, rather than merely marking shared family vulnerabilities, is the central challenge of any observational study of this kind. The researchers deployed two complementary designs. First, they compared maternal autoimmune diseases with paternal autoimmune diseases during the same pregnancies. Because fathers share genes and household environments with their children but cannot influence fetal development through the intrauterine route, a paternal signal would suggest familial confounding. Instead, paternal autoimmune diseases showed essentially no association with offspring mortality, while the maternal association remained strong, and the maternal-to-paternal hazard ratio reached 1.40 for any autoimmune disease and 2.73 for type 1 diabetes.

Second, cousin comparisons, in which offspring of sisters discordant for autoimmune disease were contrasted while stratifying on the maternal grandmother, partially controlled for shared genetics and early-family environment. These analyses attenuated the overall association to a hazard ratio of 1.04, though the confidence interval widened considerably because far fewer informative comparisons were available. Maternal type 1 diabetes retained a substantially elevated estimate even in this restricted sample, at a hazard ratio of 2.63. Taken together, the authors argue, the family-based evidence is consistent with the hypothesis that shared familial factors alone do not fully explain the findings, leaving room for genuine intrauterine mechanisms, while acknowledging that extrauterine pathways tied to pregnancy and the postnatal period cannot be excluded.

To probe those mechanisms, the team turned to formal mediation analysis within a counterfactual framework, asking whether adverse birth outcomes carry the excess risk from maternal disease to offspring death. Preterm birth emerged as the dominant candidate, mediating an estimated 53 percent of the all-cause association and roughly three-quarters of the association with perinatal-cause deaths, though wide confidence intervals counsel caution about the precise magnitude. Small for gestational age birth mediated a smaller but notable share, about 17 percent of all-cause mortality and 24 percent of perinatal deaths, while congenital heart disease accounted for around 7.5 percent. Large for gestational age, intriguingly, mediated nothing, suggesting the effect runs through restricted growth and early delivery rather than through fetal overgrowth.

The biological logic supporting these findings is well established in developmental science. Chronic maternal inflammation, immune dysregulation and transplacental autoantibody transfer can damage placental function and disrupt fetal development, producing structural and physiological alterations that heighten vulnerability in the first weeks of life. In pregnancies complicated by type 1 diabetes, metabolic and inflammatory disturbances compound one another. Notably, the cohort was born from 2001 onward, an era in which clinical management of autoimmune disease in pregnancy improved substantially, yet excess early-life mortality persisted, indicating that suboptimal care alone is unlikely to explain the pattern. Sex-stratified analyses also hinted at greater vulnerability in boys, with a 28 percent increased risk in males versus 14 percent in females, echoing the well-documented male disadvantage in perinatal survival.

The study’s limitations temper but do not overturn its conclusions. Register data cannot capture diagnoses made exclusively in primary care, medication exposures during pregnancy or the full severity spectrum of maternal disease, and residual confounding by unmeasured behaviors or pregnancy management remains possible. Because only live births were included, any effect of maternal autoimmune disease on fetal loss would have been invisible, potentially underestimating the true impact. Some subgroup estimates rest on small numbers of deaths and must be treated as hypothesis-generating. Still, the authors emphasize that if confirmed, the findings identify pregnancy and the perinatal window as critical opportunities for intervention: optimizing maternal disease control before and during conception, with particular vigilance for endocrine conditions such as type 1 diabetes, alongside strengthened perinatal care, could reduce a measurable share of preventable early-life mortality.

Subject of Research: Association between maternal autoimmune diseases during pregnancy and offspring mortality from birth to young adulthood

Article Title: Maternal autoimmune diseases during pregnancy and mortality up to young adulthood in offspring: a register-based cohort study

Article References: Zhang, H., Janszky, I., Arkema, E. V., Möller, J., Liang, Y., Mo, X., & László, K. D. (2026). Maternal autoimmune diseases during pregnancy and mortality up to young adulthood in offspring: a register-based cohort study. eClinicalMedicine, Article 104237. https://doi.org/10.1016/j.eclinm.2026.104237

Image Credits: AI Generated

DOI: 10.1016/j.eclinm.2026.104237

Keywords: maternal autoimmune disease, offspring mortality, type 1 diabetes, perinatal outcomes, preterm birth, congenital anomalies, Swedish national registers, cohort study, intrauterine mechanisms, epidemiology, fetal development, autoimmune thyroiditis