Comparison of hOCT1 mRNA levels using original (OCT3F) and new (OCT3FN) primers. CML patients with undeleted M420 showed no differences in the mRNA expression using either primer, whereas the mRNA levels of patients heterozygous for the M420del almost doubled using the new primer. In M420del homozygotes, hOCT1 was detectable with the new primers but not with the original set. UPN indicates unique patient number.