Citrullination of proteins by members of the peptidyl arginine deiminase (PAD) family of enzymes (primarily PAD4 but PAD2 and PAD3 are also involved) is a characteristic feature of disease (Harris et al. 2008), and the resulting neo-epitopes elicit an immune response via a mechanism that shares some similarity to the pathogenesis of celiac disease (Molberg and Sollid 2006). This evidence concerns the gene PADI4 and celiac disease.