PCR analysis of Pa methylation of an individual patient before and during IFNα treatment. Genomic DNA was cut with BamHI (1), Msp I (2), Bgl II (3), Sac II (4), and Hpa II (5) and processed for the Pa methylation assay (see Fig 1B). The patient diagnosed in the accelerated phase was classified as pattern C. Six months later, under IFNα therapy, pattern B was evident, and 23 months after diagnosis, the methylation pattern was A.