Multiple sclerosis among first- and second-generation immigrants in Denmark: a population-based cohort study

Nete Munk Nielsen*, Giulia Corn, Morten Frisch, Egon Stenager, Nils Koch-Henriksen, Jan Wohlfahrt, Melinda Magyari, Mads Melbye

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review

Abstract

Multiple sclerosis is a disease with a highly variable incidence worldwide. While knowledge about multiple sclerosis risk factors has grown over the years, the aetiology of multiple sclerosis has still not been fully established. We examined multiple sclerosis incidence rates among first-generation immigrants in Denmark, a high-incidence country, and their Danish-born children (second-generation immigrants), to evaluate the importance and timing of exposure to environmental factors in the aetiology of multiple sclerosis. By means of the Danish Civil Registration System we identified 9 121 187 individuals living in Denmark between 1968 and 2015, including 1 176 419 first-generation and 184 282 second-generation immigrants. Study participants were followed for multiple sclerosis in the Danish Multiple Sclerosis Registry from 1968 to 2015. The relative risk (RR) of multiple sclerosis according to immigration status was estimated by means of multiple sclerosis incidence rate ratios obtained in log-linear Poisson regression analysis. Altogether, 16 905 cases of multiple sclerosis were identified in the study cohort, 578 among first-generation and 106 among second-generation immigrants. Multiple sclerosis risk among first-generation immigrants whose parents were born in low, intermediate and high multiple sclerosis risk areas were 21% (RR = 0.21; 95% CI: 0.16-0.28), 43% (RR = 0.43; 95% CI: 0.36-0.50) and 75% (RR = 0.75; 95% CI: 0.67-0.83), respectively, of that among ethnic Danes (test for trend P < 0.0001). First-generation immigrants arriving in Denmark before age 15 years had a multiple sclerosis risk higher than that in their country of birth but lower than that in Denmark, reaching on average 69% of the multiple sclerosis risk among ethnic Danes (RR = 0.69; 95% CI: 0.55-0.87). Multiple sclerosis risk among individuals who came to Denmark at a later age remained closer to that of their country of birth, corresponding to 45% of the multiple sclerosis risk among ethnic Danes (RR = 0.45; 95% CI: 0.41-0.49). Our study supports the idea that environmental factors exerting their role in childhood or adolescence may be of aetiological relevance in multiple sclerosis.

Original languageEnglish
JournalBrain : a journal of neurology
Volume142
Issue number6
Pages (from-to)1587-1597
ISSN0006-8950
DOIs
Publication statusPublished - Jun 2019

Fingerprint

Denmark
Cohort Studies
Population
Incidence
Emigration and Immigration
Environmental Exposure

Keywords

  • age at immigration
  • cohort study
  • Denmark
  • first- and second-generation immigrants
  • multiple sclerosis

Cite this

Munk Nielsen, Nete ; Corn, Giulia ; Frisch, Morten ; Stenager, Egon ; Koch-Henriksen, Nils ; Wohlfahrt, Jan ; Magyari, Melinda ; Melbye, Mads. / Multiple sclerosis among first- and second-generation immigrants in Denmark : a population-based cohort study. In: Brain : a journal of neurology. 2019 ; Vol. 142, No. 6. pp. 1587-1597.
@article{0eacaa47f74a4f6b8e8fa37e568c7ae0,
title = "Multiple sclerosis among first- and second-generation immigrants in Denmark: a population-based cohort study",
abstract = "Multiple sclerosis is a disease with a highly variable incidence worldwide. While knowledge about multiple sclerosis risk factors has grown over the years, the aetiology of multiple sclerosis has still not been fully established. We examined multiple sclerosis incidence rates among first-generation immigrants in Denmark, a high-incidence country, and their Danish-born children (second-generation immigrants), to evaluate the importance and timing of exposure to environmental factors in the aetiology of multiple sclerosis. By means of the Danish Civil Registration System we identified 9 121 187 individuals living in Denmark between 1968 and 2015, including 1 176 419 first-generation and 184 282 second-generation immigrants. Study participants were followed for multiple sclerosis in the Danish Multiple Sclerosis Registry from 1968 to 2015. The relative risk (RR) of multiple sclerosis according to immigration status was estimated by means of multiple sclerosis incidence rate ratios obtained in log-linear Poisson regression analysis. Altogether, 16 905 cases of multiple sclerosis were identified in the study cohort, 578 among first-generation and 106 among second-generation immigrants. Multiple sclerosis risk among first-generation immigrants whose parents were born in low, intermediate and high multiple sclerosis risk areas were 21{\%} (RR = 0.21; 95{\%} CI: 0.16-0.28), 43{\%} (RR = 0.43; 95{\%} CI: 0.36-0.50) and 75{\%} (RR = 0.75; 95{\%} CI: 0.67-0.83), respectively, of that among ethnic Danes (test for trend P < 0.0001). First-generation immigrants arriving in Denmark before age 15 years had a multiple sclerosis risk higher than that in their country of birth but lower than that in Denmark, reaching on average 69{\%} of the multiple sclerosis risk among ethnic Danes (RR = 0.69; 95{\%} CI: 0.55-0.87). Multiple sclerosis risk among individuals who came to Denmark at a later age remained closer to that of their country of birth, corresponding to 45{\%} of the multiple sclerosis risk among ethnic Danes (RR = 0.45; 95{\%} CI: 0.41-0.49). Our study supports the idea that environmental factors exerting their role in childhood or adolescence may be of aetiological relevance in multiple sclerosis.",
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author = "{Munk Nielsen}, Nete and Giulia Corn and Morten Frisch and Egon Stenager and Nils Koch-Henriksen and Jan Wohlfahrt and Melinda Magyari and Mads Melbye",
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Multiple sclerosis among first- and second-generation immigrants in Denmark : a population-based cohort study. / Munk Nielsen, Nete; Corn, Giulia; Frisch, Morten; Stenager, Egon; Koch-Henriksen, Nils; Wohlfahrt, Jan; Magyari, Melinda; Melbye, Mads.

In: Brain : a journal of neurology, Vol. 142, No. 6, 06.2019, p. 1587-1597.

Research output: Contribution to journalJournal articleResearchpeer-review

TY - JOUR

T1 - Multiple sclerosis among first- and second-generation immigrants in Denmark

T2 - a population-based cohort study

AU - Munk Nielsen, Nete

AU - Corn, Giulia

AU - Frisch, Morten

AU - Stenager, Egon

AU - Koch-Henriksen, Nils

AU - Wohlfahrt, Jan

AU - Magyari, Melinda

AU - Melbye, Mads

PY - 2019/6

Y1 - 2019/6

N2 - Multiple sclerosis is a disease with a highly variable incidence worldwide. While knowledge about multiple sclerosis risk factors has grown over the years, the aetiology of multiple sclerosis has still not been fully established. We examined multiple sclerosis incidence rates among first-generation immigrants in Denmark, a high-incidence country, and their Danish-born children (second-generation immigrants), to evaluate the importance and timing of exposure to environmental factors in the aetiology of multiple sclerosis. By means of the Danish Civil Registration System we identified 9 121 187 individuals living in Denmark between 1968 and 2015, including 1 176 419 first-generation and 184 282 second-generation immigrants. Study participants were followed for multiple sclerosis in the Danish Multiple Sclerosis Registry from 1968 to 2015. The relative risk (RR) of multiple sclerosis according to immigration status was estimated by means of multiple sclerosis incidence rate ratios obtained in log-linear Poisson regression analysis. Altogether, 16 905 cases of multiple sclerosis were identified in the study cohort, 578 among first-generation and 106 among second-generation immigrants. Multiple sclerosis risk among first-generation immigrants whose parents were born in low, intermediate and high multiple sclerosis risk areas were 21% (RR = 0.21; 95% CI: 0.16-0.28), 43% (RR = 0.43; 95% CI: 0.36-0.50) and 75% (RR = 0.75; 95% CI: 0.67-0.83), respectively, of that among ethnic Danes (test for trend P < 0.0001). First-generation immigrants arriving in Denmark before age 15 years had a multiple sclerosis risk higher than that in their country of birth but lower than that in Denmark, reaching on average 69% of the multiple sclerosis risk among ethnic Danes (RR = 0.69; 95% CI: 0.55-0.87). Multiple sclerosis risk among individuals who came to Denmark at a later age remained closer to that of their country of birth, corresponding to 45% of the multiple sclerosis risk among ethnic Danes (RR = 0.45; 95% CI: 0.41-0.49). Our study supports the idea that environmental factors exerting their role in childhood or adolescence may be of aetiological relevance in multiple sclerosis.

AB - Multiple sclerosis is a disease with a highly variable incidence worldwide. While knowledge about multiple sclerosis risk factors has grown over the years, the aetiology of multiple sclerosis has still not been fully established. We examined multiple sclerosis incidence rates among first-generation immigrants in Denmark, a high-incidence country, and their Danish-born children (second-generation immigrants), to evaluate the importance and timing of exposure to environmental factors in the aetiology of multiple sclerosis. By means of the Danish Civil Registration System we identified 9 121 187 individuals living in Denmark between 1968 and 2015, including 1 176 419 first-generation and 184 282 second-generation immigrants. Study participants were followed for multiple sclerosis in the Danish Multiple Sclerosis Registry from 1968 to 2015. The relative risk (RR) of multiple sclerosis according to immigration status was estimated by means of multiple sclerosis incidence rate ratios obtained in log-linear Poisson regression analysis. Altogether, 16 905 cases of multiple sclerosis were identified in the study cohort, 578 among first-generation and 106 among second-generation immigrants. Multiple sclerosis risk among first-generation immigrants whose parents were born in low, intermediate and high multiple sclerosis risk areas were 21% (RR = 0.21; 95% CI: 0.16-0.28), 43% (RR = 0.43; 95% CI: 0.36-0.50) and 75% (RR = 0.75; 95% CI: 0.67-0.83), respectively, of that among ethnic Danes (test for trend P < 0.0001). First-generation immigrants arriving in Denmark before age 15 years had a multiple sclerosis risk higher than that in their country of birth but lower than that in Denmark, reaching on average 69% of the multiple sclerosis risk among ethnic Danes (RR = 0.69; 95% CI: 0.55-0.87). Multiple sclerosis risk among individuals who came to Denmark at a later age remained closer to that of their country of birth, corresponding to 45% of the multiple sclerosis risk among ethnic Danes (RR = 0.45; 95% CI: 0.41-0.49). Our study supports the idea that environmental factors exerting their role in childhood or adolescence may be of aetiological relevance in multiple sclerosis.

KW - age at immigration

KW - cohort study

KW - Denmark

KW - first- and second-generation immigrants

KW - multiple sclerosis

U2 - 10.1093/brain/awz088

DO - 10.1093/brain/awz088

M3 - Journal article

C2 - 31081503

AN - SCOPUS:85066968679

VL - 142

SP - 1587

EP - 1597

JO - Brain

JF - Brain

SN - 0006-8950

IS - 6

ER -