A co-twin control study of in utero exposure to poly- and perfluoroalkyl substances and associations with neonatal thyroid-stimulating hormone

Effects of Early-life PFAS Exposure on Child Neurodevelopment: A Review of the Evidence and Research gaps

PURPOSE OF REVIEW

Per- and polyfluoroalkyl substances (PFAS) are persistent chemicals with many modern applications, leading to widespread contamination and universal human exposure. PFAS exposure during early life is of particular concern, given susceptibility of the developing fetal and infant brain to toxic exposures. This review aims to synthesize current evidence, discuss methodological challenges, and highlight research gaps to guide future studies on the impact of PFAS on neurodevelopment.

RECENT FINDINGS

Sixty-one studies in total were published from 2008 to March 2024, with 35 in the last five years. Findings primarily link early life PFAS exposure to reduced cognitive, motor, and language development in infancy and increased behavioral issues like hyperactivity in childhood. Large studies have shown mixed results concerning child cognition, executive function, autism, and ADHD, with some indicating no association or unexpected protective findings. Sex-specific associations have been observed, but not consistently. Most research has addressed low-level exposure, suggesting subtle but potentially significant population-wide neurodevelopmental effects. Recent research also highlights concerns about newer, alternative PFAS, suggesting they too might affect neurodevelopment.  The effects of early-life PFAS exposure on neurodevelopment merit further study, particularly the cumulative effects of prenatal and postnatal exposures. Research has not fully explored sensitive subgroups or potential mitigating factors such as breastfeeding and nutrient intake, which will require larger, more diverse samples. Future directions include deeper study of PFAS mixtures, interactions with other neurotoxic environmental chemicals, and effects of newer PFAS types. There is also a need to focus on neuropsychological functioning in later childhood, using direct assessments for more reliable evaluations.

Thyrotoxic Effects of Mixed Exposure to Perfluorinated Compounds: Integrating Population-Based, Toxicogenomic, Animal, and Cellular Evidence to Elucidate Molecular Mechanisms and Identify Potential Effector Targets

Perfluoroalkyl and polyfluoroalkyl substances (PFAS) are emerging environmental endocrine disruptors that may adversely affect the human endocrine system, particularly the thyroid gland, the largest endocrine gland in the human body. An epidemiologic survey was conducted involving 318 community residents in Shanghai, China, to assess PFAS exposure levels. The relationship between PFAS exposure and five thyroid function indicators was analyzed using Bayesian Kernel Regression (BKMR) and Weighted Quantile Sum Regression (WQS). Ten effector genes related to PFAS and thyroid diseases were identified through the Comparative Toxicogenomics Database (CTD) for bioinformatics analysis and pathways involved were explored through mediation analysis. In vivo validation of these effector genes was conducted using PCR, complemented by in vitro cellular experiments involving transcriptome sequencing and the construction of animal models to simulate mixed PFAS exposure in the general population. Mixed PFAS exposure was found to impact thyroid health primarily through pathways related to lipid metabolism in toxicogenomic studies and resulted in the upregulation of key genes associated with lipid metabolism in animal models. Our results demonstrate that PFAS exposure could affect the expression of lipid metabolism pathways through the modulation of transcription factors, contributing to the development of thyroid disease.

Prenatal phthalate exposure and neurodevelopmental differences in twins at 2 years of age

BACKGROUND

Previous studies of singletons evaluating prenatal phthalate exposure and early neurodevelopment reported mixed results and the associations could be biased by parental, obstetrical, and genetic factors.

METHODS

A co-twin control design was employed to test whether prenatal phthalate exposure was associated with children's neurocognitive development. We collected information from 97 mother-twin pairs enrolled in the Wuhan Twin Birth Cohort between March 2016 and October 2018. Fourteen phthalate metabolites were measured in maternal urine collected at each trimester. Neurodevelopmental differences in twins at the age of two were examined as the outcome of interest. Multiple informant model was used to examine the covariate-adjusted associations of prenatal phthalate exposure with mental development index (MDI) and psychomotor development index (PDI) scores assessed at 2 years of age based on Bayley Scales of Infant Development (Second Edition). This model also helps to identify the exposure window of susceptibility.

RESULTS

Maternal urinary levels of mono-2-ethyl-5-oxohexyl phthalate (MEOHP) (β = 1.91, 95% CI: 0.43, 3.39), mono (2-ethyl-5-hydroxyhexyl) phthalate (MEHHP) (β = 1.56, 95% CI: 0.33, 2.79), and the sum of di-(2-ethylhexyl) phthalate metabolites (∑DEHP) (β = 1.85, 95% CI: 0.39, 3.31) during the first trimester showed the strongest and significant positive associations with intra-twin MDI difference. When stratified with twin chorionicity, the positive associations of monoethyl phthalate (MEP), monoisobutyl phthalate (MiBP), mono-n-butyl phthalate (MBP), monobenzyl phthalate (MBzP), individual DEHP metabolites, and ∑DEHP exposure during pregnancy with intra-twin neurodevelopmental differences were more significant in monochorionic diamniotic (MCDA) twins than those in dichorionic diamniotic (DCDA) twins.

CONCLUSIONS

Neurodevelopmental differences in MCDA twins were strongly associated with prenatal phthalate exposure. Our findings warrant further confirmation in longitudinal studies with larger sample sizes.