Familial risk of early- and late-onset multiple sclerosis: a Swedish nationwide study

BACKGROUND: Persons who develop multiple sclerosis (MS) at a young age may bear a higher genetic risk load than persons who develop MS later in life; however, the contribution of familial influence to the risk of MS, in relation to onset age, has not been established. OBJECTIVE: To investigate the familial risk of MS at two extremes of the spectrum of MS onset age: early onset (first MS symptom < 18 years of age) and late onset (first MS symptom ≥ 50 years). METHODS: Nationwide registries in Sweden were used to identify cases of MS and controls, and their familial relations. We estimated the odds ratio (OR) of an MS diagnosis for individuals with a relative diagnosed with early-onset or late-onset MS compared with those whose relatives did not have MS, using a nested case–control design. RESULTS: 629 early-onset and 1148 late-onset MS patients were identified and matched to 10 controls from the general population by age and sex. The OR of MS for individuals with a first-degree relative diagnosed with early-onset MS was 10.86 (95% CI 6.87–17.17); and for late-onset MS was 8.08 (95% CI 6.12–10.67). CONCLUSIONS: Our findings demonstrate no substantial differences in familial risk in persons with early- and late-onset MS.