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Aim  To evaluate the relationship between diagnosis and clinical course of Tourette syndrome and group A Streptococcus (GAS).

Method  GAS infections, anti-streptococcal, and anti-basal ganglia antibodies (ABGA) were compared between 168 patients (136 males, 32 females) with Tourette syndrome; (median [range] age [25th–75th centile] 10y [8–11y]); median Tourette syndrome duration (25th–75th centile), 3y (1y 3mo–5y 9mo) and a comparison group of 177 patients (117 males, 60 females) with epileptic or sleep disorders median age [25th–75th centile], 10y [8y–1y 6mo]). One hundred and forty-four patients with Tourette syndrome were followed up at 3-month intervals; exacerbations of tics, obsessive–compulsive symptoms, and other psychiatric comorbidities were defined by a bootstrap procedure. The effect of new GAS infections and identification of new ABGA upon risk of exacerbation was assessed using logistic regression analysis.

Results  Cross-sectionally, patients with Tourette syndrome exhibited a higher frequency of GAS infection (8% vs 2%; p=0.009), higher anti-streptolysin O (ASO) titres (246 [108–432] vs 125 [53–269]; p<0.001), and higher ABGA frequency (25% vs 8%; p<0.001) than the comparison group. On prospective analysis, ASO titres were persistently elevated in 57% of patients with Tourette syndrome; however, new infections or newly identified ABGA did not predict clinical exacerbations (all p>0.05).

Interpretation  Patients with Tourette syndrome might be more prone to GAS infections and develop stronger antibody responses to GAS, probably as a result of underlying immune dysregulation. New GAS infections are unlikely to exert, years after their onset, a major effect upon the severity of neuropsychiatric symptoms.