In contrast to other inflammatory myopathies (ie, dermatomyositis and polymositis), IBM is associated with earlier onset of distal weakness, increased frequency of bulbar dysfunction, and refractoriness to immunosuppressive therapy.185 Recent findings supportive of antigen-driven mechanisms include distinct haplotype associations, intramuscular infiltrates of clonally restricted CD4 and plasma cells,186 and the recent finding that ∼1/3 of patients with IBM have antibodies against cytosolic 5′-nucleotidase 1A (cN-1A).187. This evidence concerns the gene NT5C1A and myopathy.