RFC polymorphism, outcome, and relation to chromosome 21. (A) Outcome in patients with a normal copy number of chromosome 21. Patients with an increased copy number of chromosome 21 (expected higher MTX influx) had no significant differences among RFC variants (P = .94; data not shown). (B) Different hazard ratios compared with patients with a normal copy number of chromosome 21 and RFC80 GA/GG variant according to the NOPHO 92 protocol.