Background Peptidil arginine deiminase IV (PAD 4) is the responsible enzyme for a posttranslational modification called citrullination, originating the antigenic determinant recognized by anti-cyclic citrullinated peptide antibodies (aCCP)1. Four SNPs (single nucleotide polymorphisms) have been described in PADI4 gene to form a susceptibility haplotype for rheumatoid arthritis (RA)2; nevertheless results in association studies appear contradictory in different populations.
Objectives The aim of the study was to analyze if the presence of three SNPs in PADI4 gene susceptibility haplotype (GTG) is associated with aCCP antibodies positivity in patients with RA
Methods This was a transversal study that included 86 RA patients and 98 healthy controls. Polymorphisms PADI4_89, PADI4_90 and PADI4_92 in the PADI4 gene were genotyped by three polymerase chain reaction-restriction fragment length polymorphisms (PCR_RFLPs) protocols designed by us using Oligo 0.4 software, BLAST, and NEBcutter V.2.0. Haplotype analysis was done using the software PHASE for haplotype reconstruction, and recombination rate estimation using the genotypic data. a-CCP antibodies (IgG) were measured using a commercially available second generation enzyme-linked immuno sorbent assay. Clinical parameters included, DAS-28, HAQ-DI and RARBIS Indexes. For statistical analysis allelic and genotypic frequencies were determined by gene count. Cases and control groups were compared using X2 test. Hardy-Weinberg equilibrium was tested.
Results The susceptibility haplotype (GTG) was more frequent in RA patients. There were no associations between polymorphisms presence and high score punctuation in Spanish HAQ-DI and DAS-28, but we did find an association between the RARBIS index and both polymorphisms PADI4_89 and PADI4_90. We could not confirm an association between susceptibility haplotype presence and aCCP antibodies positivity.
Conclusions Further evidence about the proteomic expression of these genes finally will determine the level of participation of these genes and polymorphisms in the antigenic generation in a system with tendency to autoimmunity.
Vossenaar, E.R., et al., The presence of citrullinated proteins is not specific for rheumatoid synovial tissue. Arthritis Rheum, 2004. 50(11): p. 3485-94.
Suzuki, A., et al., Functional haplotypes of PADI4, encoding citrullinating enzyme peptidylarginine deiminase 4, are associated with rheumatoid arthritis. Nat Genet, 2003. 34(4): p. 395-402.
Disclosure of Interest None Declared