PTPN22 and rheumatoid arthritis: have shown that in Jurkat T cells transduced with plasmids carrying the mutated LYP, and in PBMC obtained from rheumatoid arthritis (RA) patients homozygous for the risk allele, the Arg620*Trp substitution makes the protein more susceptible to intracellular degradation and therefore the variant leads to weaker inhibitory effects (19).