PIK3C2A and arthritic joint disease: Although CPK levels were not well related with arthritis score (R = 0.422, Figure 2B), arthritis score showed a weak correlation with body weight change [body weight change was calculated with the following formula: body weight change (%) = body weight at each week (kg)/body weight before immunization (kg) × 100] (R = −0.610, Figure 2C) and a stronger correlation with creatinine levels (R = −0.799, Figure 2D).