IL17A and rheumatoid arthritis: A crucial role is played by Polymorphisms in the IL17A and IL17F genes, which are genetic factors linked to the susceptibility to RA (rheumatoid arthritis), the course of the disease, and the response to treatment.29 The IL-17F 7488A/G polymorphism causes a His-to-Arg substitution at amino acid 161 and is found in the 3rd exon of the IL17F gene (H161R).