Environmental factors in Tourette syndrome.

Environmental exposures during the prenatal period, perinatal stages, and postnatal life may contribute to onset and course of Tourette syndrome (TS). Pregnancy-related noxious exposures may be more frequent in pregnancies of children who will develop TS, particularly maternal smoking and prenatal life stressors. Lower birth weight and use of forceps at delivery may be associated with tic severity in the offspring; moreover, low birth weight and maternal smoking during pregnancy may affect the risk of co-morbid attention-deficit/hyperactivity and obsessive-compulsive disorders. Group A streptococcal infections as risk-modifier for TS has not been convincingly demonstrated to date, although an interaction with stressors was suggested. The PANDAS hypothesis is currently undergoing a nosological revision. Only limited anecdotal evidence supports a link of TS to other pathogens. Nevertheless, the relationship between infections and TS may be complex. Recent data point to intrinsically altered immune regulation in TS, which might predispose to both infections and autoimmune mechanisms; however, evidence of cell-mediated and antibody-mediated autoimmunity in TS is still insufficient. Psychosocial stress remains the most important contextual factor influencing tic severity, as confirmed by prospective studies. This might in part be related to enhanced reactivity of the stress response in TS patients, the mechanisms of which need to be explored further. New studies on large prospective cohorts of patients of different age and the identification of reliable biomarkers or endophenotypes indicating early, prenatal exposure to environmental insults are needed.