PRTN3 and incontinentia pigmenti: The aims of this study were (a) to describe the prevalence and co-occurrence of RF, ACPA and anti-CarP antibodies in patients with IP, (b) to investigate the relationship between anti-CarP antibody status and both disability and disease activity measured over time in patients presenting with IP, (c) to investigate these relationships in ACPA-positive and ACPA-negative subgroups and (d) to describe the additional predictive information provided by measuring these antibodies.