12th Congress of the European Hematology ... - Haematologica

12 th Congress of the European Hematology Association
er, the molecular pathogenesis of most IE cases remains unclear, with the
vast majority of cases being negative for the V617F JAK2 mutation.
Recently, four novel acquired mutations located in JAK2 exon 12 have
been described in V617F-negative individuals presenting with a myeloproliferative
syndrome characterised in part by an isolated erythrocytosis.
These mutations are located around 80 amino acids upstream of V617
and confer Epo-independent growth to erythroid progenitors in vivo.
Aims. To determine the frequency of JAK2 exon 12 gain-of-function mutations
in IE patients with low to normal serum Epo levels, and to identify
any consequences of these mutations. Methods. DNA was isolated
from peripheral blood and screened by allele-specific PCR (AS-PCR) for
the F537-K539delinsL, H538QK539L, K539L and N542-E543del JAK2
mutations. Potential JAK2 mutations were confirmed by direct sequencing
granulocyte DNA. Erythroid progenitor cells from patient peripheral
blood mononuclear cells were cultured in the presence and absence of
Epo. Bone marrow morphology was assessed on haematoxylin- and
eosin-stained sections prepared from trephines taken at diagnosis. Results.
Eight of the 58 IE patients screened were positive for a JAK2 exon 12
mutation, five of whom had the N542-E543del allele. All affected individuals
presented with a low serum Epo concentration, and fulfilled the
diagnostic criteria for IE. The haematological features of mutation-positive
and mutation-negative patients were similar, although Epo-independent
erythroid cell growth occurred exclusively in the mutation-positive
patients (p