Introduction

West syndrome is a type of developmental and epileptic encephalopathy that typically starts developing before the age of 2 years. It is characterized by the triad of epileptic spasms, hypsarrhythmia, and developmental stagnation or regression1. Various etiologies have been reported for West syndrome development; however, there have been several cases with an unknown etiology2. The most common cause of West syndrome is hypoxic-ischemic encephalopathy during the perinatal period3. A report from the United Kingdom Infantile Spasms Study, which included both infantile spasms and West syndrome, revealed that 61% of affected patients had a confirmed etiological diagnosis. Among them, hypoxic-ischemic encephalopathy was reported in 10%, followed by chromosomal abnormalities (8%), complex malformation syndromes and perinatal stroke (8%), tuberous sclerosis (7%), periventricular leukomalacia (5%), and hemorrhage (5%). Although the cause was unknown in the remaining patients, a genetic etiology was established in a few cases3. Recently, with the development of advanced genetic testing such as whole exome analysis, there has been an increase in the number of studies on West syndrome with a genetic etiology2,4,5. Furthermore, although various causative genes have been identified in most cases, genetic abnormalities vary and are rarely inherited from parents2,4,5. Therefore, other environmental factors during pregnancy may contribute to such abnormalities.

Volatile organic compounds (VOCs), including benzene, toluene, xylene, and isoprene, are chemicals that easily evaporate at room temperature. Acute somatic manifestations of VOC exposure include eye irritation/watering, nose/throat irritation, headache, nausea/vomiting, dizziness, and narcosis. Moreover, some types of chronic VOC exposures have been reported to cause cancer as well as disturbances of the liver, kidney, endocrine function, and central nervous system6,7.

Exposure to a certain component of VOCs is genotoxic to individuals, and occupational exposure to VOCs potentially containing benzene might be associated with DNA damage8. Additionally, VOCs and their metabolites can easily cross the placental barrier and reach the fetus9; however, the effects of VOC exposure on fetuses remain unknown. A previous large cohort study analyzed how occupational exposure to VOCs during pregnancy influenced childhood behavior and observed increased externalizing behavior in children who were prenatally exposed to solvents10. Toluene embryopathy is a severe condition caused by fetal exposure to toluene, resulting in growth and developmental deficiencies, abnormal craniofacial features, and abnormalities in other organs11.

Therefore, we hypothesized that VOCs cause genetic/epigenetic abnormalities in the fetus, leading to epilepsy development during early infancy. This study aimed to identify the relationship between occupational maternal exposure to VOCs and West syndrome development in children.

Results

Based on the diagnosis of epilepsy, participants were classified into three groups: those who had never been diagnosed with epilepsy (group N), those diagnosed with West syndrome (group W), and those diagnosed with epilepsy other than West syndrome (group O). Among the 88,280 participants, 15 children (0.017%) were categorized into group W, 154 into group O, and 88,111 into group N. In total, 40,870 mothers (46.3%) had used at least one VOC: 14,608 mothers had used “kerosene, petroleum, petroleum benzine, gasoline,” 33,484 mothers had used a “permanent marker,” 22,595 mothers had used a “water-based paint or inkjet printer,” and 7,855 mothers had used “other organic solvents.” Table 1 presents the distribution categorized by usage of VOCs and epilepsy syndrome.

Table 1 Distribution categorized by the usage of volatile organic compounds and the number of children with epilepsy.
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Multivariate logistic regression analysis revealed significant associations of using a “permanent marker” or “water-based paint or inkjet printer” with West syndrome development (Table 2).

Table 2 Multivariate logistic regression analysis of volatile organic compounds with respect to the risk of epilepsy syndrome.
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In total, 37,073 mothers had used a “permanent marker” or “water-based paint or inkjet printer,” while 51,207 never used any of these. Additionally, 14,434 had used only a “permanent marker,” 3,526 had used only a “water-based paint or inkjet printer,” and 19,113 had used both. Among the children who developed West syndrome, nine were born to mothers who had used both a “permanent marker” and “water-based paint or inkjet printer,” one was born to a mother who had used only a “permanent marker,” and five were born to mothers who had used neither. None of the children who developed West syndrome were born to mothers who had used only a “water-based paint or inkjet printer.” Therefore, a multivariate analysis was performed on the association between the frequency of usage of “permanent marker” and the development of West syndrome and other epilepsies. For this, the mothers who had used a “permanent marker” were further categorized into three groups: “never used” (reference), “one to three times a month,” and “one or more times a week.” Analysis of group W revealed an increased odds ratio (OR) of the incidence of West syndrome with an increased frequency of usage (one to three times a month: OR = 2.58, 95% confidence interval [CI] 0.75–8.90; one or more times a week: OR = 4.34, 95% CI 1.23–15.26), although the OR in mothers with low frequency of usage was not significant. Contrastingly, there was no significant difference in group O (one to three times a month: OR = 0.87, 95% CI 0.59–1.28, one or more times a week: OR = 0.82, 95% CI 0.50–1.35) (Table 3).

Table 3 Multivariate logistic regression analysis of the frequency of usage of permanent marker with respect to epilepsy syndrome.
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 Discussion

To our knowledge, this is the first study to use a large-scale nationwide birth cohort in Japan to examine the relationship between maternal occupational usage of VOCs and the development of West syndrome in children. We found an association of the maternal usage of a permanent marker, water-based paint, or an inkjet printer during pregnancy with West syndrome development in children. Specifically, frequent usage of a permanent marker was associated with West syndrome development.

West syndrome is an infantile developmental and epileptic encephalopathy characterized by a triad of epileptic spasms, hypsarrhythmia, and developmental stagnation or regression1. An Australian large population-based study reported that the incidence of West syndrome was 26.5/100,000 live births/year12, A similar incidence of 16–45/100,000 live births/year has also been reported13,14 in other countries. The incidence rate observed in our study is comparable to those in previous reports, suggesting that the data are reliable for West syndrome despite the use of a questionnaire in the Japan Environment and Children’s Study (JECS). West syndrome is known to develop before the age of 2 years, with several studies analyzing data up to this age. However, an analysis of the cumulative incidence among children aged < 16 years15 revealed that 27% of cases with developmental and epileptic encephalopathy developed at an age ≥ 3 years. Nevertheless, not all West syndrome cases were included in this study.

Infants with West syndrome may have an underlying etiology; however, there have been limited reports regarding the associated etiological proportions. Further, over one-third of children with infantile spasms, including those with West syndrome, may have an unknown etiology despite thorough investigation16. A recent study reported that 73% of patients with infantile spasms had a known etiology2; among them, 63% had a genetic etiology. Therefore, to analyze the pregnancy-related environmental risk factors for West syndrome development, we excluded four patients with specific etiologies (holoprosencephaly, tuberous sclerosis complex, microcephaly, and neonatal hypoxic-ischemic encephalopathy). Additionally, three of the fifteen participants were found to have a genetic etiology; however, we were unable to obtain their details. The remaining 12 participants either had no genetic etiology or had not undergone genetic testing.

Most West syndrome cases have a genetic etiology, with many of them being considered to be de novomutations2,4,5,17,18. Numerous studies have focused on the molecular mechanisms underlying the pathogenesis of genetic variants19,20,21; however, some patients still have an unknown etiology. Moreover, there have been limited studies on how the genetic etiology develops with respect to the maternal environment. In this study, we found that frequent usage of permanent marker was associated with West syndrome development. Alcohols are the most commonly emitted organic solvents from permanent markers22. Maternal alcohol exposure that results in the development of epilepsy in children is a known fetal alcohol spectrum disorder (FASD)23. There are several reports on the effects of alcohol on the development of epilepsy. In a study that analyzed DNA methylation patterns in children with FASD, the methylation change resulted in an overrepresentation analysis of genes with up-methylated cytosine-phosphate-guanines, which can cause epilepsy24. In another study in which a pathological analysis was performed, a reduction in the number of cells in the hippocampus, which may have lowered the seizure threshold, was observed25. However, FASD is an effect of maternal oral intake of alcohol. To the best of our knowledge, a review of existing literature revealed no studies on exposure to alcohol as a volatile substance, as in the present study. The other products, such as inkjet printers, analyzed in this study may also contain alcohol. Castorina et al.22. reported that permanent markers have higher rates of alcohol emissions than dry erase markers and highlighters22. However, the alcohol content and emission rates of these products vary considerably, making it challenging to discuss them in a generalizable manner. In this study, we analyzed the frequency of usage of daily necessities, which does not directly correlate with the amount of exposure. To elucidate the relationship between exposure and the use of supplies, it is essential to analyze the emitted amount of these products, as in the study by Castorina et al.22. Although we could not identify the specific candidate VOCs associated with West syndrome development, some VOCs have been shown to affect the central nervous system. Two postulated mechanisms may underlie their effects on the central nervous system: genetic toxicity and oxidative stress26. For example, benzene covalently binds to DNA and induces genetic toxicity. Moreover, when left unrepaired, this genetic toxicity disrupts the cellular microenvironment, inhibits important enzymes, induces cell death, and causes other cellular abnormalities27,28. Recent studies using a comet assay have revealed the genetic toxicity of other VOCs, including toluene, xylene, and ethylbenzene29. However, these VOCs, especially benzene, toluene, and xylene, are not used as solvents for markers in Japan. Benzene, toluene, xylene, and benzaldehyde are known to generate reactive oxygen species (ROS)30,31, which are crucial in regulating various physiological functions. Excessive ROS production causes oxidative stress, which is associated with various diseases32,33. Some studies have highlighted the potential effects of oxidative stress on the fetus, particularly through the ovaries. Oxidative stress in the lipids of oocytes is assumed to be the cause of persistently poor oocyte quality following exposure to toxicants during early life34. Moreover, although there are reports of the association of DNA damage and oxidative stress with malignant tumors in adults35, their effects on fetuses remain unclear. Additionally, VOCs are known to easily cross the placenta9, resulting in impaired neuronal development and malformations36. Genetic toxicity and oxidative stress may also affect the fetus.

The association between environmental factors and infantile spasm development remains unclear. However, a retrospective study showed that the onset of infantile spasms was more than twice as likely to occur during months with a short photoperiod, suggesting that environmental photoperiodic factors might affect infantile spasm development37. Moreover, a meta-analysis revealed that latitude predicted the incidence of infantile spasms38. Animal studies have also revealed an association between prenatal stress and infantile spasm development39. Prenatal stress exposure may affect hormone levels and neurotransmitter receptor expression, potentially causing N-methyl-D-aspartic acid-induced spasms40. Occupational exposure to organic solvents has been shown to affect seizures in exposed individuals. A case series on adult patients reported that epileptic seizures occurred after exposure to a mixture of solvents. They assumed a chronological relationship between organic solvents exposure and epilepsy; however, they could not define the mechanism and did not mention how it affected offspring41,42.

This study has several limitations. First, data regarding the frequency of maternal VOC usage were collected as a substitute for assessing the maternal exposure to VOCs. Therefore, it is difficult to conclude that maternal exposure was accurately assessed. Second, since the information was collected using a questionnaire, it was difficult to ensure data consistency. VOC concentrations in daily necessities, including permanent markers, varied and were not considered in this study. Qualitative and quantitative analysis of the VOCs in the air during exposure to identify candidate chemical(s) that may show temporal association(s) is essential to accurately investigate the effects of VOCs on the human body. Third, other possible maternal exposure sources during pregnancy or postnatal exposure of the children were not considered. Finally, we could not determine whether using daily necessities contributed to West syndrome development or whether the workplace environment or other environmental factors affected it.

Until now, there has been insufficient evidence regarding environmental factors associated with the development of epilepsy in children. Our study highlights a significant association between the maternal frequent usage of permanent markers and West syndrome development. However, future studies are warranted to clarify how environmental factors influence the development of epilepsy, including whether it is caused by the exposure to chemicals, if chemicals are the causative factor, and how they affect the human body.

Methods

We utilized data from a large-scale cohort study, the JECS, which is a government-funded birth cohort study that began in January 2011, to elucidate the relationship between environmental factors and maternal and infant health43,44. During a 3-year period that concluded in March 2014, 103,060 pregnancies and 104,062 fetal records were extracted from 15 regional centers, which represented the diverse Japanese social, economic, and urban realities. The JECS protocol was reviewed and approved by the Ministry of Environment’s Institutional Review Board on Epidemiological Studies (ethical approval number: 100910001) and Ethics Committees of all participating institutions. The JECS was conducted following the tenets of the Declaration of Helsinki and other national regulations and guidelines. All participants provided written informed consent.

Data collection

The study cohort data were extracted from the “jecs-ta-20190930” and “jecs-qa-20210401” datasets released in October 2019 and April 2021, respectively. The datasets comprised 104,062 fetal records and 100,303 live birth records.

To assess occupational maternal exposure to VOCs, data regarding maternal usage of VOCs were collected using a questionnaire completed during the second or third trimester of pregnancy45. Additionally, data on maternal age at birth, gestational age, and child sex were transcribed from medical records.

VOCs were defined as volatile chemicals emitted from the organic solvents used in work environments. A questionnaire was administered to assess occupational usage of VOCs, which were divided into four categories. In these four categories, the self-administered questionnaire was answered after grouping participants with similar daily necessities, to account for their actual use in daily life and work45. The questionnaire included the following question: “Check the frequency of using or handling the following materials during work for more than half of the day since becoming pregnant. 1) kerosene, petroleum, petroleum benzine, gasoline; 2) permanent marker; 3) water-based paint or inkjet printer; and 4) other organic solvents (e.g., paint thinner, solvent for examination/analysis/extraction, dry-cleaning solvent, stain-removing agent, paint coating, nail polish remover, etc.).” Participants had to select one of the following four responses based on the frequency of use: “never,” “one to three times a month,” “one to six times a week,” or “every day.” Participants who selected “never” were classified into the “never used” group, while those who selected “one to six times a week” or “every day” were classified into the “used one or more times a week” group.

Information on epilepsy was collected using a two-step process. First, parents were asked whether their child had ever been diagnosed with epilepsy in a self-report questionnaire when the child reached the age of 2 years. Subsequently, detailed information was collected from attending physicians for children with confirmed diagnoses. The diagnosis and classification of epilepsy syndromes were based on the International League Against Epilepsy classification of epileptic seizures and syndromes46.

Of the 100,303 live births, we excluded participants with multiple births (n = 1,891). Among the 98,412 birth records, 10,128 were excluded due to missing data regarding maternal usage of VOCs and incomplete answers for the variables. Additionally, to focus on environmental risk factors for West syndrome development, we excluded patients with structural, infectious, metabolic, or immunologic etiologies (n = 4). Ultimately, 88,280 children were included in the analysis (Fig. 1).

Fig. 1
figure 1

Flowchart of the study participants.

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Statistical analysis

Statistical analyses were performed using JMP Pro 16 software for Windows (SAS Institute Inc., Cary, NC, USA). To analyze the relationship between each VOC and epilepsy (Table 2), the OR was calculated for VOCs used one or more times a month. The total number of participants who chose “one to three times a month,” “one to six times a week,” and “every day” was used. A logistic regression model was utilized to calculate the adjusted OR and 95% CI to assess the association between VOC usage and other variables. Variables included in the model were selected based on previously published literature47, maternal occupation, and biological validity. Maternal occupations were categorized as full-time homemaker, professional and technicians, clerical support workers, service workers, and others. The biological variables included maternal age at birth, gestational age, and child sex. The significance level was set at p < .05.