In conclusion, the present work provides valuable information on the role of the PADI4 polymorphisms 89G>A, 90T>C, and 92G>C, and their haplotypes, which are associated with susceptibility to RA in our study population, and the susceptibility haplotype (GTG) is related with a greater increase in PADI4 mRNA and more significant PAD4 activity. The gene discussed is PADI4; the disease is rheumatoid arthritis.