Figure 1 (A) Methylated methylation‐specific polymerase chain reaction (M‐MSP) and unmethylated methylation‐specific poylmerase chain reaction (U‐MSP) of p15 in primary chronic lymphocytic leukaemia (CLL) samples. B, reagent blank; N, normal marrow DNA controls; P, methylated positive control; patients 1, 2, 3 and 6, primary CLL marrow samples. (B) Sequence of positive control M‐MSP product and (C) sequence of M‐MSP of the primary CLL marrow sample. Wildtype (WT) cytosine (C) residues that remained unchanged in methylated CpG are coloured blue and underlined, whereas those that were changed to thymidine (T) are coloured red and underlined. U‐MSP shows that the methylated control (M) was totally methylated.