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Birth cohort effects in multiple sclerosis
Ya-Ping Jin1, Jesús De Pedro-Cuesta, Gonzalo López-Abente
1Neuroepidemiology Unit, Division of Neurology, Karolinska Institute, Huddinge University Hospital, S-141 86, Huddinge, Sweden. Ya-Ping.Jin@neurotec.ki.se
Purpose:
To identify potential birth cohort effects in multiple sclerosis in Sweden and particularly in Stockholm county.
Methods:
Data on multiple causes of death from multiple sclerosis during 1962 to 1995 in Sweden and 1968 to 1995 in Stockholm county were analyzed using age-period-cohort models and curvature.
Results:
Mortality from multiple sclerosis was higher in Sweden than in Stockholm county, with stable time trends, slight period effects and marked age effects. Cohorts born before or after a central period, from 1910 through 1930, registered lower mortality. A periodic wave-form mortality pattern was identified, following a 5-to-6-year cycle for cohorts born before 1925 both in and outside Stockholm county, and changing to longer or irregular cycles for cohorts born after 1930.
Conclusions:
Although methodological constraints inducing the saw-tooth pattern cannot be excluded, these results are consistent with etiologic hypotheses claiming a role for environmental factors in multiple sclerosis.