Mi-2 antibodies

• Autoantibodies which have a diagnostic and predictive value in myositides, especially in dermatomyositis. The Mi-2-AK are directed against 2 largely identical, 220 kDa proteins (Mi-2a and Mi-2b) of a nucleosome remodeling and deacetylase complex. The complex catalyzes changes in the chromatin structure and thus access to DNA for transcription factors. This results in its function as a transcription activator or repressor.
• Depending on the method, the prevalence of anti-Mi-2 in dermatomyositis is 5-33%, in polymyositis 0-10% and in inclusion body myositis 0-8%.

The specificity of Mi-2 Ak for idiopathic myositis in general reaches 97%. Its predictive value is considered high for the diagnosis of dermatomyositis (DM). This statement also seems to be valid for juvenile DM. There is a close correlation between the occurrence of Mi-2 autoantibodies and the HLA feature DR7. Patients with Mi-2 autoantibodies generally show a milder course of disease, seem to respond well to glucocorticoid therapy and have a relatively good prognosis. The assumption that Mi-2 AK could serve as exclusion criterion for paraneoplastic myositis (dermatomyositis) has not yet been confirmed.