Abstract

Chronic myeloproliferative disorders (CMPDs) are clonal hematopoetic stem cell disorders resulting in the increased production of cells of the myeloid lineage. The recently described G to T point mutation at nucleotide 1849 in the JAK2 gene may be a specific molecular marker to aid in the diagnosis of CMPDs, including polycythemia vera (PV), essential thrombocythemia (ET), and chronic idiopathic myelofibrosis (CIMF). Previously described methods of detection for this point mutation include sequencing, allele-specific PCR, and restriction digestion. We report here the development of a novel method to detect the JAK2 point mutation using high resolution amplicon melting curve analysis. Genomic DNA was obtained from peripheral blood samples from patients with PV, ET, CIMF, and suspected CMPD using the Qiagen DNA Blood kit (Valencia, CA). DNA was quantified using PicoGreen (Invitrogen) fluorescent dye followed by spectrophotometry and samples were normalized to a standard concentration. Real time PCR was performed on the Roche Light Cycler in the presence of the double stranded DNA binding dye LCGreen1 using primers that flank the point mutation. High Resolution Melting curve analysis was then performed on the HR-1 instrument (Idaho Technologies), and mutation status assigned by comparing the melting curve position and shape to controls of known mutation status. For comparison, the samples were also restriction digested using BsaX I and analyzed by agarose gel electrophoresis. Mutation status was confirmed by sequencing of the PCR amplicons (Lark Technologies, Houston, TX) for a subset of specimens. Twenty six patients with known CMPD as defined by the WHO criteria (2001) were included in the study. In addition, seven patients with suspected CMPD were studied. The point mutation in JAK2 was identified in 9 (100%) of 9 PV patients, 7 (58%) of 12 ET patients, 1 (50%) of 2 CIMF patients, 3 (100%) of 3 CMPD NOS patients, and 2 (29%) of 7 patients with suspected CMPD. Patients testing homozygous for the JAK2 mutation included 6 patients with PV, 1 patient with ET, and 1 patient with CMPD, NOS; all other positive patients were heterozygous for the mutation. We observed excellent correlation between the melting curve analysis and restriction digest results. High resolution melting curve analysis is a rapid, sensitive, low reagent cost method to assess for the JAK2 point mutation in cases of suspected or known CMPDs. The advantages of this technique include the ability to discriminate heterozygous from homozygous mutations, increased sensitivity as compared to sequencing, rapid turn around time, no post-amplification modification, and the ability to screen for other mutations or polymorphisms within exon 12 of the JAK2 gene.

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