Strong association between myotonic dystrophy type 2 and autoimmune diseases.

Background: Myotonic dystrophy type 2 (DM2) is a dominantly inherited multisystem disorder, characterised by progressive proximal weakness, myotonia, cataracts and cardiac conduction abnormalities. Our clinical impression of an association between DM2 and autoimmune diseases or autoantibody formation has not been published previously.

Objective: The aim of the present study was to investigate the frequency of autoimmune diseases and serum autoantibodies in patients with DM2 compared with patients with adult onset myotonic dystrophy type 1 (DM1).

Methods: 28 genetically proven Dutch DM2 patients participated in the study and were compared with 51 age and sex matched adult onset DM1 patients. As the primary outcome measure, the presence of an autoantibody or autoreactive T cell associated autoimmune disorder was assessed. As a secondary outcome measure, the presence of autoantibodies in serum (nuclear and non-nuclear antibodies) was assessed in all patients.

Results: The frequency of autoimmune diseases (21% vs 2%) and the frequency of autoantibodies (25% vs 2%) were both significantly (p<0.01) higher in DM2 patients compared with DM1 patients. Data on DM1 patients were comparable with the general population. Results were not confounded by smoking, medication use, familial clustering, age or sex.

Conclusion: The results provide new insight into the clinical picture of DM2. In addition, possible explanations for the association between DM2 and autoimmune diseases are proposed.