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Are Autoantibodies Against the β1-adrenergic Receptor Markers for Dilated Cardiomyopathy? by Ragna Arndt-Marić, Herbert Nägele, Gabriele Schewe, Arno Kromminga

Background: Dilated cardiomyopathy (DCM) is one of the leading causes of heart failure in the western world but there is still no specific and early diagnosis available. Besides a genetic predisposition and viral infections, autoimmune reactions play an important role in the pathogenesis of DCM. The β1-adrenergic receptor (β1-AR) has been described as the major target structure in autoimmune DCM.
Methods: In this study a recombinant GST-β1-AR fusion protein comprising the second extracellular loop was generated as a target for the analysis of autoantibodies in sera from 115 patients with different heart failure diseases (41 DCM, 30 non-ischemic secondary cardiomyopathy [NISCM], 44 coronary artery disease [CAD]). Sera were collected from a non-selected population of heart failure patients in consecutive order.
Results: Autoantibodies against the β1-AR were detected in 37 % of DCM, 30 % of NISCM, and 36 % of CAD patients but none of the controls were positive. Furthermore, our data show that cardiomyopathy patients with anti- β1-AR antibodies are younger (54 years vs. 61 years [DCM], 53 years vs. 56 years [NISCM], 61 years vs. 61 years [CAD]. Regardleβ of diagnosis antibody-positive patients had lower EF levels ( 29 % vs. 32 %, p = 0.0001 [DCM]; 23 % vs. 25 %, p < 0.0001 [NISCM]; 23 % vs. 25 %, p < 0.0001 [CAD]) than the antibody-negative counterparts but, nevertheleβ, also lower NT-proBNP levels compared to antibody negative patients (567 pg/mL vs. 1296 pg/mL, p = 0.0005 [DCM]; 224 pg/mL vs. 1135 pg/mL, p = 0.0002 [NISCM]; 605 pg/mL vs. 940 pg/mL, p = 0.0005 [CAD]).
Conclusions: We conclude that DCM patients should be further characterized and differentiated by the detection of autoantibodies against β1-AR. Autoimmune DCM patients are younger compared with their non-autoimmune counterparts, poβibly due to the autoimmune trigger of the disease or reflecting an early stage of the disease. Surprisingly, the autoimmune patients have worse clinical manifestations but show leβ exceβive NT-proBNP levels. It is not clear yet, though, whether these autoantibodies have a direct impact on the NT-proBNP levels. Whether or not these data are a consequence of pathogenic antibodies has to be elucidated in further studies.

DOI: Clin. Lab. 2010;56:519-526