封入体筋炎と自己抗体

Sporadic Inclusion Body Myositis and Autoantibodies

孤発性封入体筋炎は，手指屈筋や大腿四頭筋の筋力低下と筋萎縮を特徴とする筋疾患であるが，原因は不明で治療法は未確立である。本疾患の病態として，炎症と変性機序のクロストークが推測されるが，病態解明の端緒と期待されるのが近年本患者に同定されたサイトゾル5’-ヌクレオチダーゼ1Aに対する自己抗体である。本抗体は特異度の点から診断に有用であるとともに，直接的に筋変性を誘導する可能性が推測される。

Abstract

Sporadic inclusion body myositis (sIBM) is a chronically progressing inflammatory myopathy most common in the aged population. Asymmetric muscle weakness and waste of the quadriceps and finger and wrist flexor muscles are characteristic features of sIBM. Histological findings suggest the involvement of a crosstalk of inflammatory and myodegenerative mechanisms in the pathogenesis of sIBM. As an etiological clue to sIBM, identification of autoantibodies against cytosolic 5'-nucleotidase 1A (NT5C1A) in plasma and serum samples from patients with sIBM has been attracting attention. So far, various methods with clinical utility have been established to detect anti-NT5C1A autoantibodies. The measurement of the autoantibodies is useful for the diagnosis of sIBM due to its high specificity. Moreover, the autoantibodies may have pathogenic roles in the development of the disease by stimulating catabolic conditions and/or causing dysfunction in protein degradation of skeletal muscles; however, the molecular mechanisms by which the sarcoplasmic autoantigen is recognized and involved in the degeneration of myofibers remain unclear.