GSTM1 and juvenile idiopathic arthritis: In a subgroup of JIA patients who did not achieve remission during MTX therapy, statistically significant difference in frequency of GSTM1 deletion polymorphism was detected between subgroup with one or more changes of biologic disease modifying drugs (bDMARD) compared to the subgroup with one bDMARD in terms of achieving remission: 64.3% to 28.6%; P=0.026.