Abstract
BACKGROUND: Several studies analyzing the season of birth of multiple sclerosis (MS) patients have suggested birth in spring as a risk factor for MS. OBJECTIVE: To determine if risk of MS in Oslo is associated with season of birth, and to find out whether this association differs by generation, gender or MS phenotype onset (Relapse-remitting and Primary progressive). METHODS: Patients with MS born between 1901 and 1990 registered in the Oslo MS registry were included (n=1658). The control sample was composed of the live birth records in the same time period in Norway. A chi square test was used to compare the distributions of MS births over months and quarters versus controls. Patients were subdivided into 30-year cohorts, gender - and MS phenotype groups for separate analyses. RESULTS: Only second quarter MS births during 1961-1990 were associated with an increased risk of MS (+24%, p = 0.0009). The increase in second quarter births derived entirely from RR-MS cases. There was an increase in second quarter RR-MS births during 1901-1930 (+26%, p = 0.038), and 1961-1990 (+27%, p = 0.0009) compared with the expected birth distribution. There was no increase in second quarter births during 1931-1960 (-2%, p = 0.773). There was no difference in this effect between genders. CONCLUSION: This study confirms previous reports of increased MS births in spring, limited to the Relapse Remitting phenotype and to certain generations. This suggests that early developmental processes that are dependent on vitamin D can influence both MS susceptibility and phenotype.
BACKGROUND: Several studies analyzing the season of birth of multiple sclerosis (MS) patients have suggested birth in spring as a risk factor for MS. OBJECTIVE: To determine if risk of MS in Oslo is associated with season of birth, and to find out whether this association differs by generation, gender or MS phenotype onset (Relapse-remitting and Primary progressive). METHODS: Patients with MS born between 1901 and 1990 registered in the Oslo MS registry were included (n=1658). The control sample was composed of the live birth records in the same time period in Norway. A chi square test was used to compare the distributions of MS births over months and quarters versus controls. Patients were subdivided into 30-year cohorts, gender - and MS phenotype groups for separate analyses. RESULTS: Only second quarter MS births during 1961-1990 were associated with an increased risk of MS (+24%, p = 0.0009). The increase in second quarter births derived entirely from RR-MS cases. There was an increase in second quarter RR-MS births during 1901-1930 (+26%, p = 0.038), and 1961-1990 (+27%, p = 0.0009) compared with the expected birth distribution. There was no increase in second quarter births during 1931-1960 (-2%, p = 0.773). There was no difference in this effect between genders. CONCLUSION: This study confirms previous reports of increased MS births in spring, limited to the Relapse Remitting phenotype and to certain generations. This suggests that early developmental processes that are dependent on vitamin D can influence both MS susceptibility and phenotype.