The possible effects of different forms of LYP on rheumatoid arthritis (RA). Left, illustration of LYP isoforms: LYP_v1 has four P motifs, but LYP_v2 lacks the P2, P3, and P4 motifs. Healthy patients (top) have a balance of LYP protein isoforms (indicated by the scales and number of proteins shown, left); they tend to have a lower frequency of the W620 allele (R620W variant) of PTPN22 and a higher frequency of the Q263 allele (R263Q variant) (right), which leads to a low risk of RA. Ronninger et al.  have shown that the ratio of the long (LYP_v1) and short (LYP_v2) isoforms of PTPN22 is significantly higher in RA patients (bottom) than in controls, and RA patients have a higher frequency of the W620 allele and a lower frequency of the Q263 allele. These differences might lead to greater inflammation in RA patients.