Anti‐NT5C1A antibody seropositive IBM patients had a higher frequency of finger flexion weakness (91% vs. 76%; P < 0.01), but no significant differences were seen with regard to age at onset, maximum CK level, dysphagia, or complications of other autoimmune diseases/sarcoidosis/malignancy (Table 3, Table S3). Here, NT5C1A is linked to autoimmune disease.