Analysis of the influence of endocrine-disrupting chemicals on autism spectrum disorder through different research approaches

Autism spectrum disorder (ASD) is a neurodevelopmental condition with a complex pathophysiology, including impaired social communication skills and repetitive behaviors. The genetic contribution includes rare highly penetrant variants and a high number of single nucleotide variants representing low risk factors for ASD. Genes linked to ASD have been proposed to converge onto a few core intracellular molecular pathways, each necessary for correct neurodevelopment. Recently it has been proposed that exposure to environmental factors, such as endocrine-disrupting chemicals (EDCs), may concur to disease onset. However, the assessment of chemical exposure, as well as the correlation with potential adverse consequence on neurodevelopment, are two very challenging issues. Indeed, exposure in real-life is long-term, spanning from gestation to adulthood, substances are many and mixed, and interact with highly variable individual genetic backgrounds. In this thesis I will present three approaches to investigate the effects of EDCs on mammalian neurodevelopment. One approach dedicated to human subjects is based on cohort studies. These have accumulated the evidence of environmental exposure associated to adverse health outcomes, despite many intrinsic limitations. The case-control study that I take into consideration investigates the possible correlation between EDCs levels, heavy metals concentrations and steroid hormones activities detected in amniotic fluids, and increased ASD risk. The presence of some perfluoroalkyl substances (PFAS) and heavy metals is detectable in amniotic fluid, indicating another type of exposure in addition to blood one. ASD cases showed different pattern regarding PFAS and heavy metals levels. Despite the lack of robust statistical significance, the study suggests a role of EDCs exposure on ASD risk. Interestingly, the authors showed that PFAS were inversely associated to ASD risk, perhaps due to PFAS weak estrogenic and anti-androgenic activities. Another approach relies on experimental evidence using animal models. To investigate whether bisphenol-A (BPA) and genistein, two known EDCs, may be related to the onset of autistic-like behaviors, mice were prenatally exposed to these and monitored in adult life with appropriate tests. Mice treated with BPA showed increased repetitive behaviors, while those exposed to genistein showed socio-communicative disturbances. Lastly, experiments on human cells are used to evaluate the effects of exposure of mixtures of EDCs on gene expression profiles. Mixes were predefined based on the presence of EDC in maternal body fluids associated with children born with language delay or low-body weight. Interestingly, human induced pluripotent stem cells (iPSC) treated with two specific mixes (N and G) showed changes in global gene expression enriched in disease-genes associated with intellectual disability and ASD (mix N) or with adipogenesis/obesity (mix G). In conclusion, these approaches allow to move towards more robust evidence that endocrine disruptors play a role in ASD onset with the future possibility of evaluating the specific risk for each individual according to the genetic background.