Season of birth and multiple sclerosis in Tunisia.

BACKGROUND: Recent studies on date of birth of multiple sclerosis (MS) patients showed an association between month of birth and the risk of developing MS. This association has not been investigated in an African country. OBJECTIVE: We aimed to determine if the risk of MS is associated with month of birth in Tunisia. METHODS: Data concerning date of birth for MS patients in Tunisia (n = 1912) was obtained. Birth rates of MS patients were compared with all births in Tunisia matched by year of birth (n = 11,615,912). We used a chi-squared analysis and the Hewitt's non-parametric test for seasonality. RESULTS: The distribution of births among MS patients compared with the control population was not different when tested by the chi-squared test. The Hewitt's test for seasonality showed an excess of births between May and October among MS patients (p = 0.03). The peak of Births of MS patients in Tunisia was in July and the nadir in December. CONCLUSION: Our data does support the seasonality hypothesis of month of birth as risk factor for MS in Tunisia. Low vitamin D levels during pregnancy could be a possible explanation that needs further investigation.