title: Season of birth and multiple sclerosis in Tunisia.
abstract: 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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Neurology, Research Unit 12SP21, Razi Hospital, Tunis, Tunisia.
authors.forename: Youssef
authors.initials: Y
authors.lastname: Sidhom
authors.affiliation: Department of Neurology, Research Unit 12SP21, Razi Hospital, Tunis, Tunisia.
authors.forename: Imen
authors.initials: I
authors.lastname: Kacem
authors.affiliation: National Health Insurance Fund, Tunis, Tunisia.
authors.forename: Lamia
authors.initials: L
authors.lastname: Bayoudh
authors.affiliation: Department of Neurology, Research Unit 12SP21, Razi Hospital, Tunis, Tunisia.
authors.forename: Mouna
authors.initials: M
authors.lastname: Ben Djebara
authors.affiliation: Department of Neurology, Research Unit 12SP21, Razi Hospital, Tunis, Tunisia.
authors.forename: Yosr
authors.initials: Y
authors.lastname: Hizem
authors.affiliation: National Health Insurance Fund, Tunis, Tunisia.
authors.forename: Sami
authors.initials: S
authors.lastname: Ben Abdelfettah
authors.affiliation: Department of Neurology, Research Unit 12SP21, Razi Hospital, Tunis, Tunisia.
authors.forename: Amina
authors.initials: A
authors.lastname: Gargouri
authors.affiliation: Department of Neurology, Research Unit 12SP21, Razi Hospital, Tunis, Tunisia. Electronic address: riadh.gouider@gnet.tn.
authors.forename: Riadh
authors.initials: R
authors.lastname: Gouider
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D002648:Child; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009103:Multiple Sclerosis / Q000453:epidemiology*; D036801:Parturition; D012042:Registries; D012307:Risk Factors; D012621:Seasons; D014416:Tunisia; D055815:Young Adult
keywords: Month of birth; Multiple sclerosis; North Africa; Seasonality; Tunisia; Vitamin D