Mutation profile of JAK2 transcripts in patients with chronic myeloproliferative neoplasias

Abstract

Here, we describe the JAK2 mutation profile in a series of approximately 20,000 blood samples from patients with clinically suspected myeloproliferative neoplasias. Using a sensitive reverse transcription-PCR and direct sequencing approach on RNA rather than DNA, we detected JAK2 mutations in exons 12-15 in approximately 20% of these patients. We identified new mutations in addition to the known V617F and exon 12 mutations, which were the most common. Most of the novel mutations are located in the pseudokinase domain and therefore are expected to relieve the autoinhibitory function of this domain on JAK2 kinase activity. Our data suggest that molecular testing of JAK2 mutations should not be restricted to the V617F and exon 12 mutations, but perhaps should extend to most of the pseudokinase domain coding region as well. Furthermore, mutation screening using RNA is highly sensitive and could replace DNA-based testing because of the relative abundance of target transcripts and the ease in detecting deletion of the entire exon.

Figure 1

Schematic diagram of the JAK2 gene structure. A: JAK2 protein contains JAK homology domains 1 through 7 (JH1-JH7) with the JH2 pseudokinase domain highlighted in black. The corresponding exon regions are also shown. All mutated residues in exons 12–15 discovered in this report are indicated with mutation hotspots labeled in red. B: Representative sequencing chromatograms of some novel mutations. R564L and G571S in exon 13, the deletion of entire exon 14, and L624P in exon 15 are shown. Positions of mutant nucleotides are indicated by arrowheads and deleted nucleotides by dots.