CALCITONIN-GENE METHYLATION IN CHRONIC MYELOPROLIFERATIVE DISORDERS

Alterations in DNA methylation appear to be an integral part of the ma lignant transformation. For example, the p15 region of chromosome 11 w ith multiple genes related to cell growth regulation exhibits differen t methylation patterns in the 5' area of the calcitonin A gene in heal thy bone marrow cells, and in leukemic cell populations. In this work the methylation status of the 5' area of the calcitonin gene in myelop roliferative disorders (MPD) other than chronic myeloid leukemia (CML) is studied. A total number of 37 patients with polycythemia vera, ess ential thrombocythemia, or myelofibrosis were studied. A control group of 18 healthy persons and patients with reactive hematologic changes was included. The DNA isolated from peripheral blood or bone marrow ce lls was digested with the methylation-sensitive Hpall restriction enzy me. A Southern blot was hybridized with a 1.7 kb probe specific to the 5' area of the calcitonin gene. The result was visualized autoradiogr aphically and analyzed with a densitometer. The results have been expr essed as ratios between the abnormal and normal autoradiography band i ntensities, referred to as the calc-value or CALC. An increase in the calc-value signifies increasing methylation. In the control group the calc-value had a mean of 0.274. The myelofibrosis patients exhibited v ery strong hypermethylation in the calcitonin gene 5' area, with a mea n calc-value of 11.1 (median 2.6). The polycythemia vera patients show ed considerable variation in their methylation status, with a mean val ue of 1.52. The essential thrombocythemia patients exhibited weak hype rmethylation, with a mean calc-value of 0.58. A correlation between ka ryotypic abnormalities and hypermethylation was observed. Complicated forms of MPD exhibited higher levels of methylation than the uncomplic ated disease forms.