To investigate the involvement of epigenetic regulatory mechanisms in the control of CAT expression, we quantified the methylation levels of 8 CpG sites within the CpG Island II of the human CAT gene promoter in genomic DNA from 21 CLL and 10 HD B-cell samples, using bisulfite pyrosequencing (Fig. 2A). Here, CAT is linked to B-cell chronic lymphocytic leukemia.