Risks of multiple sclerosis in relatives of patients in Flanders, Belgium

Objectives - To calculate age adjusted risks for multiple sclerosis in relatives of Flemish patients with multiple sclerosis. Methods - Lifetime risks were calculated using the maximum likelihood approach. Results - Vital information was obtained on 674 probands with multiple sclerosis in Flanders and a total of their 26 225 first, second, and third degree relatives. Full medical information to allow documentation of multiple sclerosis status was available for 21 351 (81.4%) relatives. The age adjusted risk for parents was 1.61 (SEM 0.35)%, for siblings 2.10 (SE 0.36)%, and for children 1.71 (SEM 0.70)%. For aunts and uncles, the risk was 0.66 (SEM 0.13)%. Conclusions - The risk for first degree relatives of patients with multiple sclerosis in Flanders is increased 10-fold to 12-fold; for second degree relatives, it is increased threefold. This information can be used for risk counselling in families and provides additional support for the role of more than one locus contributing to the susceptibility of multiple sclerosis.