title: Familial risk of multiple sclerosis: a nationwide cohort study.
abstract: Multiple sclerosis (MS) is known to accumulate within families. The magnitude of the familial risk, however, remains uncertain. Using a nationwide MS register and other national registers, the authors estimated relative and absolute risks of MS in a population-based cohort that included 19,615 first-degree relatives of 8,205 Danish MS patients followed from 1968 to 1997. The ratio of observed to expected numbers of MS cases served as the measure of the relative risk of MS. Lifetime risks of MS in first-degree relatives were estimated as the product of the relative risk and the national lifetime risk of MS. Overall, first-degree relatives had a sevenfold increased risk of MS (relative risk=7.1, 95% confidence interval: 5.8, 8.8) (n=90) compared with the background population. By modeling the individual incidence rate of MS as the sum of a familial component and a sporadic risk component, the familial excess lifetime risk was found to be 2.5% (95% confidence interval: 2.0, 3.2) among first-degree relatives of MS patients, irrespective of the gender of the proband and the relative. This percentage should be added to a sporadic absolute risk in the general population of 0.5% in women and 0.3% for men. Spouses of MS patients did not experience an increased risk of MS, suggesting no major role for environmental factors acting in adulthood.
authors.affiliation: Department of Epidemiology Research, Danish Epidemiology Science Centre, Statens Serum Institut, Copenhagen, Denmark. NMN@ssi.dk
authors.forename: Nete Munk
authors.initials: NM
authors.lastname: Nielsen
authors.forename: Tine
authors.initials: T
authors.lastname: Westergaard
authors.forename: Klaus
authors.initials: K
authors.lastname: Rostgaard
authors.forename: Morten
authors.initials: M
authors.lastname: Frisch
authors.forename: Henrik
authors.initials: H
authors.lastname: Hjalgrim
authors.forename: Jan
authors.initials: J
authors.lastname: Wohlfahrt
authors.forename: Nils
authors.initials: N
authors.lastname: Koch-Henriksen
authors.forename: Mads
authors.initials: M
authors.lastname: Melbye
mesh_terms: D003718:Denmark / Q000453:epidemiology; D005192:Family Health; D005260:Female; D005500:Follow-Up Studies; D020022:Genetic Predisposition to Disease; D006801:Humans; D015994:Incidence; D008297:Male; D009103:Multiple Sclerosis / Q000453:epidemiology* / Q000235:genetics*; D011159:Population Surveillance; D012189:Retrospective Studies; D012307:Risk Factors