Is season of birth associated with multiple sclerosis?

Objective - To compare the monthly distribution of multiple sclerosis (MS) patients' births with that of the Sicilian population. Background - Studies on the association between season of birth and risk of MS are scanty and controversial. Design and methods - Archives of the Institute of Neuropsychiatry of the Universities of Palermo and Catania were searched up to 1995 for definite MS patients (McDonald and Halliday criteria). The monthly distribution of MS patients' births (N = 965) was compared with that of the Sicilian population (N = 5,608,307). Results - The distribution of births among MS patients compared with the general population was not different when tested by the χ2 statistic (P > 0.25). The Hewitt's non- parametric test for seasonality showed an excess of births between June and November among MS patients (P = 0.004). Conclusion - A different pattern of MS patients' births is observed in Sicily and in Northern countries.