Dozens of studies have investigated the occurrence of other autoimmune diseases in multiple sclerosis (MS) patients and their first-degree relatives, but the only remarkable conclusion that can be drawn from such studies is their exceptional inconsistency.
The frequency of type 1 diabetes (T1D), Crohn disease (CD), ulcerative colitis (UC), Graves disease, systemic lupus erythematosus, Addison disease, pemphigoid, and others have been claimed to be elevated either in MS patients or in their relatives over the past decade. None have been confirmed, however.
For any epidemiological finding, bias, confounding, and the simple play of chance all need to be considered to see whether they can explain an observed association before interpreting results as being causally linked. One bias that has been thought to exist is surveillance bias: in this setting, autoimmune diseases would be more likely to be recognized and diagnosed in MS patients because they are in close contact with health care professionals, unlike healthy controls.
A recent study by Roshanisefat and colleagues1 investigated the risk of autoimmune disease in a large population of Swedish MS patients, their parents, and carefully matched controls. Strikingly, no consistent increased frequency for any autoimmune disease was found among parents of MS patients.
The authors did find an increased frequency of UC, CD, T1D, psoriasis, polyarteritis nodosa, and pemphigoid in MS patients—but this increase was only present after the diagnosis of MS was made. This is an elegant epidemiological analysis which highlights that surveillance bias was entirely behind the associations observed.
Such strikingly negative findings, as documented by other large population-based studies,2 unequivocally show a true absence of autoimmune disease aggregation in MS patients and their families.
References:
1. Roshanisefat H, Bahmanyar S, Hillert J, et al. Shared genetic factors may not explain the raised risk of comorbid inflammatory diseases in multiple sclerosis. Mult Scler. 2012;18:1430-1436.
2. Ramagopalan SV, Dyment DA, Valdar W, et al. Autoimmune disease in families with multiple sclerosis: a population-based study. Lancet Neurol. 2007;6:604-610.
