Prenatal and postnatal exposure to PM_2.5 and the risk of tic disorders

Tic disorders are common neurodevelopmental disorders during childhood. Whether prenatal and postnatal exposure to particulate matter with an aerodynamic diameter less than 2.5 μm (PM2.5 ) plays a role in the development of tic disorders remains unexplored.To investigate the association of exposure between PM2.5 during the pregnancy and infancy periods and the risk of tic disorders.This birth cohort study recruited singleton live births at term gestations in central Taiwan from the Taiwan Maternal and Child Health Database between 2004 and 2012 and followed up to the end of 2017. New cases of tic disorders were defined using the ICD-9-CM (307.2) and ICD-10-CM (F95), which include all tic spectrum disorders. We assigned daily PM2.5 concentrations derived from a satellite-based model to individuals based on maternal residential addresses at delivery. We fit Cox proportional hazard model and distributed lag non-linear model to estimate the associations between PM2.5 and tic disorders, with hazard ratio (HR) with 95% confidence interval (CI) as the effect measure.Of the 309,376 singleton live births at term gestations, we identified 5902 (1.9%) tic disorder cases. The HR of tic disorders was positively associated with a 10 μg/m3 increase in PM2.5 : during pregnancy HR 1.09, 95% CI 1.04, 1.15 and during infancy HR 1.12, 95% CI 1.06, 1.18. The vulnerable time window for infants with increased risk of tic disorders was 6-52 weeks after birth. We observed a nonlinear relationship between PM2.5 and the risk of tic disorders, with exposure to PM2.5 between 16 and 64 μg/m3 being associated with the risk of tic disorders. The association was restricted to Tourette's disorder group. Infant sex did not modify these associations.Infants delivered at term and exposed to PM2.5 are associated with an increased risk of tic disorders (6-52 weeks). Further studies are needed to confirm these associations.