MPL Mutation Profile in JAK2 Mutation-Negative Patients with Myeloproliferative Neoplasms.

Abstract 1891

Poster Board I-914

Myeloproliferative neoplasms (MPNs) are multipotent hematopoietic stem cell neoplasms characterized by excess production of various blood cells. Mutations in the thrombopoietin receptor gene (MPL) have been reported in JAK2 V617F-negative patients with MPNs. We evaluated the prevalence of MPL mutations relative to those of JAK2 mutations at V617 or in exons 12 through 15 in a large number of patients with suspected MPNs. A total of 2790 patients with suspected MPNs referred to our institution were first screened for JAK2 V617F and exon 12–15 mutations. Patients with no JAK2 mutations detected were then tested for MPL mutations in exons 10 and 11 by means of a sensitive MPL reverse-transcription-PCR-based assay with direct bidirectional sequencing. All JAK2 and MPL mutation assays were performed on plasma RNA, rather than DNA isolated from blood or bone marrow cells. Of the 2790 patients, 529 (18.96%) had a V617F mutation; 12 (0.43%) had small insertion/deletions in exon 12; and 7 (0.25%) had other JAK2 mutations, including point mutations in exons 13–15 and an exon 14 splice mutation. MPL mutations were identified in 66 of the 2242 (2.94%) JAK2 mutation-negative patients (2.37% of all tested patients). W515L was the dominant MPL mutant detected in 46 patients (70%) including two patients with homozygous W515L mutation. The other W515 variants (W515K, W515R, W515S, W515G, W515A, W515*) comprised 16% (N=11) of the MPL mutations. The remaining MPL mutations (n =9, 14%) were detected at other locations in exon 10 and 11. Two of these were novel exon 10 deletion/insertion mutations and two were unreported exon 11 point mutations. The exon 10 T496-A497ALVI (4AA) homozygous insertion was detected in one patient with a confirmed diagnosis of idiopathic myelofibrosis and the W515-P518 del/ins (KT) mutation was detected in another patient with unspecified MPN. The two novel MPL exon 11 point mutations were D545G and D545N. The S505N mutation (n=2) and V507I (n=1), R514K (n=1), and A519V (n=1) were also detected. Furthermore, three unreported silent polymorphisms/mutations (T496, L543, and D534) were detected. In conclusion, our results demonstrate that for every 100 V617F mutations detected in patients with MPNs, there are 2.3 JAK2 exon 12 mutations, 1.3 JAK2 exon 13–15 mutations, and 12.5 MPL mutations. Thus, MPL mutation detection should be performed on all JAK2 V617F-negative patients with suspected MPNs. In addition, our findings indicate that >20% of MPL mutations would have been missed if only W515L and W515K were analyzed; thus, sequencing of both exon 10 and 11 may be beneficial.