Contribution of a haplotype in the HLA region to anti-cyclic citrullinated peptide antibody positivity in rheumatoid arthritis, independently of HLA-DRB1.
OBJECTIVE
To examine the risk of anti-cyclic citrullinated peptide (anti-CCP) antibody positivity in rheumatoid arthritis (RA) patients carrying certain haplotypes in the HLA region.


METHODS
A total of 1,389 Japanese patients with RA were genotyped for 30 single-nucleotide polymorphisms (SNPs) in the HLA region using commercial oligonucleotide arrays (from Perlegen or Affymetrix) as well as for HLA-DRB1 alleles using a sequence-specific polymerase chain reaction method. Stepwise logistic regression was used to select from among the 30 SNPs the ones that represented a risk of anti-CCP antibody positivity. Haplotypes of the selected SNPs were inferred using an expectation-maximization algorithm. Associations of individual SNPs were evaluated with the Cochran-Armitage test for trend. DRB1 alleles and haplotypes were evaluated with the chi-square test. Heterogeneities of risks among the shared epitope (SE) and non-SE HLA-DRB1 alleles were examined using the exact test. Haplotype associations that were independent of individual HLA-DRB1 alleles were evaluated using the likelihood ratio test.


RESULTS
Significant associations were found for 9 SNPs (smallest P value being 2.4x10(-8)) and in 4 HLA-DRB1 alleles (smallest P value being 2.0x10(-10) in DRB1*0405). Stepwise logistic regression selected 4 SNPs (rs9262638, rs7775228, rs4713580, and rs9277359). Among the 16 inferred haplotypes of these 4 SNPs, 6 indicated significant associations (smallest P value being 1.9x10(-11)). Risks among SE and non-SE alleles were significantly heterogeneous (P=0.0095 and P=9.8x10(-9), respectively), indicating the importance of stratification with individual DRB1 alleles rather than SE alleles. Conditional analysis of the risk associated with individual DRB1 alleles identified a risk haplotype that was independent of DRB1 (odds ratio 2.00 [95% confidence interval 1.44-2.79], P=2.6x10(-5)).


CONCLUSIONS
Heterogeneous risks of anti-CCP antibody positivity were confirmed among SE and non-SE alleles in our patient population. A risk haplotype in the HLA region that is independent of HLA-DRB1 was confirmed.
Okada
Yukinori
Y
Institute of Medical Science, University of Tokyo, Tokyo, Japan.
Yamada
Ryo
R
Suzuki
Akari
A
Kochi
Yuta
Y
Shimane
Kenichi
K
Myouzen
Keiko
K
Kubo
Michiaki
M
Nakamura
Yusuke
Y
Yamamoto
Kazuhiko
K
D001172:Arthritis, Rheumatoid / Q000097:blood / Q000235:genetics* / Q000276:immunology*; D000939:Epitopes / Q000235:genetics; D005260:Female; D020022:Genetic Predisposition to Disease; D006684:HLA-DR Antigens / Q000235:genetics*; D059811:HLA-DRB1 Chains; D006239:Haplotypes; D006801:Humans; D008297:Male; D008875:Middle Aged; D010456:Peptides, Cyclic / Q000276:immunology*; D020641:Polymorphism, Single Nucleotide
D000939:Epitopes; D006684:HLA-DR Antigens; D059811:HLA-DRB1 Chains; D010456:Peptides, Cyclic; C487763:cyclic citrullinated peptide