Month of birth as a latitude-dependent risk factor for multiple sclerosis in Norway

Grytten, Nina; Torkildsen, Øivind; Aarseth, Jan Harald; Benjaminsen, Espen; Celius, Elisabeth Gulowsen; Dahl, Ole Petter; Holmøy, Trygve; Løken‐Amsrud, Kristin Ingeleiv; Midgard, Rune; Myhr, Kjell–Morten; Risberg, Geir; Vatne, Anita; Kampman, Margitta T.

doi:10.1177/1352458512471094

Cited by 40 publications

(40 citation statements)

References 35 publications

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“…Studies on season of birth in the Northern hemisphere have frequently reported an increased risk of MS in patients born in spring and summer and a decrease in MS births in autumn and winter months [14][15][16][17][18][19]. A pooled analysis in the largest study, based on datasets from Canada, Great Britain, Denmark and Sweden (n = 42,045) showed an excess of MS among people born in May and a relative deficit among those born in November [20].…”

Section: Discussionmentioning

confidence: 99%

Season of birth and multiple sclerosis in Tunisia

Sidhom

Kacem

Bayoudh³

et al. 2015

Multiple Sclerosis and Related Disorders

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Section: Discussionmentioning

confidence: 99%

Season of birth and multiple sclerosis in Tunisia

Sidhom

Kacem

Bayoudh³

et al. 2015

Multiple Sclerosis and Related Disorders

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“…Hence, the incidence of developing MS correlates with the risk in areas of childhood residence [4] . Additionally, studies have shown risk association during months of birth as spring births have higher risk of MS than autumn births [17] . Several environmental factors have been investigated.…”

Section: Environmental Factorsmentioning

confidence: 99%

Multiple sclerosis and the role of immune cells

Høglund

Maghazachi

2014

WJEM

135

101

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Multiple sclerosis (MS) is a complex disease with many different immune cells involved in its pathogenesis, and in particular T cells as the most recognized cell type. Recently, the innate immune system has also been researched for its effect on the disease. Hence, cells of the immune system play vital roles in either ameliorating or exacerbating the disease. The genetic and environmental factors, as well as the etiology and pathogenesis are of utmost importance for the development of MS. An insight into the roles play by T cells, B cells, natural killer cells, and dendritic cells in MS and the animal model experimental autoimmune encephalomyelitis, will be presented. Understanding the mechanisms of action for current therapeutic modalities should help developing new therapeutic tools to treat this disease and other autoimmune diseases.

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“…The month of birth effect on multiple sclerosis (MS) risk reported by numerous groups,1–3 has been interpreted as evidence of environmental exposures during the prenatal period influencing the future risk of MS. A recent publication by Fiddes et al 4. suggests that these results rather reflect the failure of adjusting for confounding factors that likely varied according to the areas and cohorts included in these studies.…”

Section: Introductionmentioning

confidence: 99%

“…The authors pointed out that no earlier studies had adequately controlled for confounding factors, and they presented analyses showing that adequately adjusting for year and place of birth would reduce confounding and most likely eliminate the month of birth effect 4. We have previously reported a month of birth effect for MS in Norway 3. The results were adjusted for year, but not place of birth.…”

Section: Introductionmentioning

confidence: 99%

Month of birth and risk of multiple sclerosis: confounding and adjustments

Torkildsen

Aarseth

Benjaminsen

et al. 2014

Ann Clin Transl Neurol

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A month of birth effect on multiple sclerosis (MS) risk has been reported from different countries. Recent critics have suggested that this finding is caused by confounding and that adequately adjusting for year and place of birth would markedly reduce this effect. All inhabitants in Norway are registered in the Norwegian Population Registry (Statistics Norway), making this an ideal area for performing adjusted analyses. Using the entire Norwegian population born between 1930 and 1979 (n = 2,899,260), we calculated the excess between observed and expected number of births for each month for 6649 Norwegian MS patients, 5711 mothers, 5247 fathers, and 8956 unaffected siblings. The analyses were adjusted for year of birth and place of birth according to the 19 counties in Norway. An unadjusted analysis revealed 13% fewer MS births than expected in February (P = 0.0015; Bonferroni corrected P = 0.018), 10% more in April (P = 0.0083; Bonferroni corrected P = 0.0996) and 15% more in December (P = 0.00058; Bonferroni corrected P = 0.007). Adjustments for both year and place of birth significantly altered our results for February and December, but even after these adjustments there were still 10% more MS births than expected in April (P = 0.00796; Bonferroni corrected P = 0.096). MS patients had a higher incidence of April births than their siblings (Fisher-exact test; P = 0.011), mothers (Fisher-exact test; P = 0.004), and fathers (Fisher-exact test; P = 0.011) without MS. Adjustments for confounding significantly affected our results. However, even after adjustments, there appears to be a persistent higher than expected frequency of April births in the MS population.

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Month of birth as a latitude-dependent risk factor for multiple sclerosis in Norway

Abstract: This study confirms previous reports of increased MS births in spring and decreased MS births in the winter months. This could support the role of decreased sunlight exposure during pregnancy and vitamin D deficiency in prenatal life in MS.

Cited by 40 publications

References 35 publications

Season of birth and multiple sclerosis in Tunisia

Season of birth and multiple sclerosis in Tunisia

Multiple sclerosis and the role of immune cells

Month of birth and risk of multiple sclerosis: confounding and adjustments

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