Hypermethylation Analysis of p16INK4a and p15INK4b Promoters in Chronic Lymphocytic Leukaemia Patients and Normal Individuals

Introduction: Chronic Lymphocytic Leukaemia (CLL) is a common type of leukaemia in persons of predominantly European descent but is rare in the Asian population. Disparities in CLL incidence among people of Asian and European descent may be related to the genetic make-up of the two different populations. Hypermethylation event might be one of the silencing mechanisms that inactivate the tumour suppressor genes in CLL. The aim of this study was to determine the hypermethylation status of p16(INK4a) and p15(INK4b) among CLL patients and normal individuals.Materials Et Methods: A total of 25 CLL patients and 25 normal individuals were recruited for this study and their genomic DNA were extracted from the peripheral blood. The hypermethylation status of p16(INK4a) and p15(INK4b) were determined using Methylation Specific-PCR (MS-PCR) whereas DNA sequencing method was applied to selected samples for validation of the MS-PCR results. We also evaluated the association between hypermethylation of these genes with the clinical and demographic characteristics of each group of subjects. Results: Among the CLL patients, p15(INK4b) partial-methylation occurred in 6 (24%) subjects while methylation occurred in 1 (4%) subject. All the remaining patients were unmethylated at p15(INK4b). All the samples showed unmethylation at p16(INK4a). Statistically significant associations were found between p15(INK4b) hypermethylation with the presence of CLL (p=0.01) and with race (p=0.02).Conclusion: Further study using a larger sample size is warranted to explore the significance of DNA methylation incidence among the CLL patients of the Malaysian population. Hence, we suggest that hypermethylation at p15(INK4b) has a huge influence that kick-starts CLL disease among Malaysians and MS-PCR technique is applicable to be used in methylation study.