Reduced DNA methylation and hydroxymethylation in patients with systemic mastocytosis

Objective: As disruption of epigenetic control is a frequent event in solid tumors and leukemia, we investigated changes in DNA methylation (5mC) and hydroxymethylation (5hmC) in patients with systemic mastocytosis (SM), a rare myeloproliferative disease with a wide spectrum of severity, characterized by the accumulation of mast cells in various organs. Methods: We measured overall genomic levels of 5hmC and 5mC in patients with SM by dot blot, as well as by quantitative immunofluorescence in samples of cutaneous mastocytosis. Results: Overall 5hmC levels were reduced in all patients with SM, but to a greater extent in the presence of higher D816V mutational load in the KIT oncogene, which affects prognosis and therapeutic options in these patients. Loss of 5hmC was likely due to systemic effects of SM as it did not correlate with overall mast cell burden in these patients, nor it was due to inactivating mutations of TET2 or reduced TET2 expression. Conclusions: The correlation between SM diagnosis and significantly low 5hmC levels suggests that reduction of 5hmC represents a systemic effect of SM that may be useful for patient stratification and that measurements of 5hmC levels may serve as a better prognostic marker than TET2 mutations.