Evidence from family studies for autoimmunity in dilated cardiomyopathy.

Organ-specific antibodies are found in patients with autoimmune disease and their symptom-free relatives many years before clinical onset. Organ-specific cardiac antibodies can be found in patients with dilated cardiomyopathy (DCM) and their relatives, which supports the idea that DCM is an autoimmune disease. We did non-invasive cardiological assessment and antibody screening in 342 symptom-free relatives (170 male, 172 female, mean [SD] age 31 [16] years). 177 relatives were from 33 families with more than 1 affected individual (familial DCM) and 165 relatives from 31 families with only 1 affected member (non-familial DCM). The frequency of cardiac antibodies was higher among relatives of DCM patients than in controls (20% vs 3.5%, p = 0.0001). In 37 (58%) of the families studied, cardiac antibodies were found in the proband and/or in at least 1 family member and were more common in familial than in non-familial DCM (24% vs 15%, p = 0.036). Antibody-positive relatives were younger (26 [15] vs 33 [17] years, p = 0.01) and had a larger mean echocardiographic left ventricular end-systolic dimension (35 [6] vs 32 [6], p = 0.01 mm) and reduced percentage fractional shortening compared with antibody-negative relatives (31 [6] vs 34 [6], p = 0.008). Presence of cardiac-specific autoantibodies in symptom-free DCM relatives provides evidence of autoimmunity in a subset of our patients (58%), including familial and non-familial forms of DCM. These antibodies are associated with mild left ventricular systolic dysfunction on echocardiography and may be early markers for relatives at risk of DCM.