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Anti-CarP antibodies linked to increased disability, disease activity in patients with RA
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Patients with rheumatoid arthritis who had anticarbamylated protein antibodies had higher disease activity and greater disability compared to patients without the antibodies, according to recently published data.
A cohort of 1,995 patients from the Norfolk Arthritis Register who were at least 16 years of age and had at least two swollen joints for at least 4 weeks were enrolled between 1990 and 2009, with the exclusion of data from patients enrolled between 1995 and 1999 who were not followed for more than 2 years.
Patients were assessed at baseline for demographics, medication details, smoking status and assessment of 51 joints. Patients completed the Health Assessment Questionnaire (HAQ). Follow-up occurred yearly for 3 years, then again at 5, 7, 10, 15 and 20 years with repeated assessments. The Disease Activity Score in 28 joints (DAS28) was calculated and blood samples were collected and frozen at baseline and every 5 years. Frozen samples were sent to the Leiden University Medical Center for analysis between 2013 and 2014 to identify anticarbamylated protein (anti-CarP) antibodies, rheumatoid factor (RF) and anticyclic citrullinated protein antibodies (ACPA).
Analysis revealed anticarbamylated protein (anti-CarP) antibodies in 460 patients (23%) and 1,476 patients were tested for anti-CarP, ACPA and RF. Of patients who had all three tests, 297 (20%) had anti-CarP antibodies, and 74 (5%) tested positive for only anti-CarP antibodies.
The median HAQ among patients with anti-CarP antibodies was 1.25 compared to 0.875 for patients without the antibodies, and the median DAS28 was 4.23 in patients with anti-CarP antibodies compared to 3.73.
Generalized estimating equations showed patients with anti-CarP antibodies were more disabled during follow-up compared to patients without the antibodies, a difference that remained significant after adjustment for ACPA or DAS28. A significant association was seen between HAQ and DAS28 in the ACPA-negative subgroup of patients with anti-CarP antibodies.
Of the 61% of patients who met American College of Rheumatology/European League Against Rheumatism (ACR/EULAR) 2010 criteria for rheumatoid arthritis (RA), anti-CarP was associated with DAS28 with significance, and a trend toward significance was observed with HAQ, while the association was significant among patients who did not meet ACR/EULAR 2010 criteria.
Two companies are currently developing routine, commercial assays to test for anti-CarP antibodies, according to the authors. – by Shirley Pulawski
Disclosure: The researchers report no relevant financial disclosures.
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