Aims Tourette syndrome is known to be usually familial (if the wider phenotype is considered) but the underlying genetic mechanism is still unknown while putative environmental factors increasing vulnerability are unknown or unproven. Hypotheses include perinatal difficulties and infection with Group A Streptococcus. There are examples of seasonality of birth as a proxy for early life environmental factors being relevant to disease causation. The aim of this study was to investigate whether the month of birth of patients with Tourette syndrome varies from the expected distribution.

Methods Data on month of birth were collected as part of a database of 240 Tourette syndrome patients attending a specialist clinic for children and adults. A data set of all recorded births in the UK from 1941 to 2000 was used for comparison with the expected seasonality of births. The number of births for each month was compared with the total of the other 11 months for cases and controls using a 2×2 χ² test. Outcomes for months that appeared significantly different from the expected number were tested using a p-value adjusted for multiple comparisons with a Bonferroni correction.

Results A degree of variation from the expected numbers for each predicted birth compared to national birth figures was observed, with peaks occurring in February and August and troughs in March and September. However, there did not appear to be an obvious seasonal trend and the observed variation in the sample was statistically insignificant for all months.

Conclusions No significant variation from the fluctuations seen in national birth data was observed for the month of birth of patients with Tourette syndrome. This suggests that seasonal environmental factors during foetal development or early life are unlikely to contribute to an increased risk of Tourette syndrome.