Prenatal exposure to Per- and polyfluoroalkyl substances and children's digit ratios based on Shanghai Minhang Birth Cohort: The role of DNA methylation in the placenta

Backgrounds Evidence on prenatal Per- and polyfluoroalkyl substances (PFAS) exposure effects on reproductive health and underlying mechanisms is limited. The digit ratio is a sensitive marker for evaluating reproductive effects.Objectives This study examined the relationship between children's digit ratios and prenatal exposure to PFAS, with potential mediation by placental DNA methylation.Methods Maternal plasma concentrations of 11 PFAS compounds (12-16 weeks of gestation) and digit ratios of children at 4 and 6 years of age were measured in 345 mother-child pairs. PFAS concentrations were determined using high-performance liquid chromatography-tandem mass spectrometry, while DNA methylation levels of five reproduction-associated genes were assessed using reduced representation bisulfite sequencing in placenta samples, including RBMX Like 2 (RBMXL2), Protocadherin8 (PCDH8), Sperm Acrosome Associated 1 (SPACA1), SPARC (Osteonectin) Cwcv And Kazal Like Domains Proteoglycan 2 (SPOCK2), and Transmembrane Protein 30B (TMEM30B). The associations of PFAS exposure with both the digit ratios and DNA methylation levels were estimated using multiple linear regression models. Mediation analysis was employed to delineate the potential mediating effects within these observed associations.Results Maternal PFAS concentrations were inversely associated with boys' digit ratios at 6 years of age. Per unit increase of ln-transformed Perfluorooctanoic acid (PFOA), Perfluorodecanoic acid (PFDA), and Perfluoroundecanoic acid (PFUdA) concentrations was associated with lower digit ratios, with the estimates being 1.41 (95% CI: -2.67, -0.16), 0.98 (95% CI: -1.85, -0.10), and 0.87% (95% CI: -1.73, -0.01), respectively. Besides, maternal PFAS exposure was inversely associated with the methylation levels of RBMXL2, PCDH8, and SPOCK2. In addition, SPOCK2 hypomethylation mediated the association between prenatal PFOS exposure and lower digit ratios among boys at 6 years of age.Discussions Our findings indicate a link between prenatal PFAS exposure and alterations in offspring digit ratios. This association may be partially explained by changes in DNA methylation.