PRTN3 and rheumatoid arthritis: The use of the classification by du Montcel and colleagues suggests a risk hierarchy in ACPA production in early RA patients: the S2 (KRAA at positions 71–74) and S3P (QRRAA or RRRAA at positions 70–74) alleles conferring predisposition, while the S1 (ARAA or ERAA at positions 71–74) and S3D (DRRAA at positions 70–74) alleles confer protection, in comparison with X (non-RAA patterns at positions 72–74).