title: Month of birth is associated with multiple sclerosis but not with HLA-DR15 in Finland.
abstract: BACKGROUND
  Spring birth has been found to be associated with increase in the risk of MS. However, this effect is reportedly found particularly in HLA-DR15 positive patients.
  
  
  OBJECTIVE
  Examine the month of birth (MOB) effect in Finnish MS patients and its association with HLA-DR15.
  
  
  METHODS
  Using the national register on hospitalizations during 1979-2004 we identified 8359 MS patients. We used a χ(2)-analysis to compare the distribution of MOB in MS patients versus age-adjusted controls. Patients were subdivided into 10-year birth cohorts to analyse temporal variations in MOB. A subgroup of HLA-typed MS patients (n = 657) and a population sample of healthy donors from the Finnish Bone Marrow Donor Registry (n = 19,805) were included to analyse connections between HLA-DR15 and MOB.
  
  
  RESULTS
  An April birth was associated with a 9.4% increased risk of MS (p = 0.008), whereas November birth was associated with an 11.1% decreased risk (p = 0.004) compared with the expected birth distribution. No temporal clustering in the MOB effect was found during 1900-1988. Both HLA-DR15 positive (34% increase, p = 0.043) and DR15 negative (48% increase, p = 0.0095) MS patients exhibited an increase in spring births (in May). HLA-DR15 in healthy subjects was not associated with MOB.
  
  
  CONCLUSIONS
  We confirm that spring birth increases MS risk. This phenomenon was not associated with HLA-DR15 and there was no evidence of temporal clustering. The MOB effect suggests that early developmental processes may modulate MS risk.
authors: Department of Neurology, Helsinki University Central Hospital and Program for Molecular Neurology, Biomedicum-Helsinki, University of Helsinki, Helsinki, Finland.
authors: Kari-Pekka
authors: KP
authors: Saastamoinen
authors: Marja-Kaisa
authors: MK
authors: Auvinen
authors: Pentti J
authors: PJ
authors: Tienari
mesh_terms: D000328:Adult; D000368:Aged; D016022:Case-Control Studies; D016009:Chi-Square Distribution; D016000:Cluster Analysis; D005260:Female; D005387:Finland / Q000453:epidemiology; D059810:HLA-DR Serological Subtypes / Q000235:genetics*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009103:Multiple Sclerosis / Q000453:epidemiology* / Q000235:genetics* / Q000276:immunology; D012042:Registries; D018570:Risk Assessment; D012307:Risk Factors; D012621:Seasons; D013997:Time Factors
chemical_list: D059810:HLA-DR Serological Subtypes; C106559:HLA-DR15 antigen