Molecular detection of gene mutations and methylation abnormalities: applications in solid tumor diagnosis

Frequent copresence of methylated DNA and fragmented nucleosomal DNA in plasma of lymphoma patients

BACKGROUND

The circulating DNA in plasma/serum of cancer patients has been shown to reflect the characteristics of the tumor DNA including molecular changes, such as methylation, point mutations and microsatellite instability. Fragmented nucleosomal DNA in plasma resulting from apoptotic death of the tumor cells may also provide an indication for tumor DNA. In this study, we comparatively analysed plasma DNA methylation and presence of fragmented nucleosomal DNA in patients with lymphoproliferative diseases.

METHODS

Methylation in the first exon of the tumor supressor gene p16 was investigated by the methylation-sensitive restriction enzyme-related PCR. DNA fragmentation in plasma was analysed by gel electrophoresis.

RESULTS

p16 gene methylation was found to occur in 73% of patients but in none of the 20 healthy controls. Nucleosomal DNA fragmentation was detectable in 81% of patients. In 67% of patients, copresence of both parameters was observed. Presence of both parameters was associated with the stage of disease which was more pronounced for nucleosomal DNA fragmentation.

CONCLUSIONS

Our results suggest that presence of methylated and apoptotic DNA in plasma of patients with lymphoproliferative diseases is a frequent event and may be used as a marker for early diagnosis and during the follow-up of the disease.