Citrullination of histones, which is a form of histone modification, is facilitated by the enzyme peptidyl arginine deiminase 4 (PAD4) across multiple species, but has not been characterized in cats44 The increase in plasma citH3 in our study suggests that PAD4, which is highly expressed in neutrophils, may be activated in cats with cardiomyopathy. Here, PADI4 is linked to cardiomyopathy.