C-reactive protein (CRP) polymorphism (rs3091244) may play a protective role against ankylosing spondylitis (AS). Also, the wild type CC haploid may be a risk factor for developing AS, according to a new study.
In several rheumatoid diseases, CRP is the most commonly used diagnostic test for detecting inflammation and progression and for determining treatment response. In previous studies inflammatory changes were associated with CRP gene polymorphism, according to the study authors at the Department of Physical Medicine and Rehabilitation at Canakkale Onsekiz Mart University, Canakkale, Turkey. Their intent in this study was to examine the association in AS patients between the CRP gene polymorphism and both clinical and laboratory findings.
Investigators included 40 AS patients and 40 controls. They determined CRP gene C, A and T alleles after real time polymerase chain reaction and calculated odds ratios for all alleles and haploids of the CRP gene.
While analysis showed that C and T allele frequencies were similar in the two groups, A allele frequency was higher in the AS group compared to the control group (38% vs. 15%). C and T allele frequencies were 68% and 26.2%, respectively in the AS group, and 57.5% and 27.5%, respectively in the control group.
CC wild allele frequency was similar in the AS and control groups, at 47.5% and 42.5%, respectively (P=1.0). Wild type C allele, CC and CT haploid frequency, however, were linked to an increased relative risk for AS, with odds ratios for the C allele at 1.6, for the CC haploid at 1.2 and for the CT haploid at 3.7.
The similar CRP levels with and without CRP gene polymorphism and the fact that some patients with severe AS had normal CRP levels may suggest that CRP gene polymorphism is not associated with CRP levels, the authors speculated.
Two other measures improved with the presence of the CRP polymorphism: chest expansion and finger-to-ground distance. “Chest expansion is related to thorax involvement and ground-place distance is related to lumbar vertebrae involvement,” the authors said, noting further that limitations of the lumbar or thoracic spine can occur in early or mild AS patients.
The study’s additional finding, alongside the AS risk conferred by the wild type CC haploid, was that CRP gene polymorphism is more common in HLA [human leukocyte antigen]-B27 negative patients, a group with reduced AS severity and progression. That finding also supports a protective role in AS for the CRP gene polymorphism, the researchers said.
Akbal A, Resorlu H, et al., The relationship between C-reactive protein rs3091244 polymorphism and ankylosing spondylitis. International Journal of Rheumatic Disease 2015.