Juvenile myelomonocytic leukemia (JMML) is a malignant hematopoietic disorder of early childhood with excessive proliferation of the myeloid and monocytic lineage. Deregulation of the RAS signal transduction pathway is thought to play a key role in its pathogenesis. We examined peripheral blood or bone marrow cells of 36 children with JMML for activating point mutations in codons 12, 13 and 61 of the NRAS and KRAS proto-oncogenes by allele-specific restriction assay, singlestrand conformation polymorphism and/or direct sequencing. Codons 12, 13 and 61 of HRAS were examined in 26 of these patients. We detected RAS mutations in six cases (17%) located at N12 (n = 2), N13 (n = 3) and K13 (n = 1). In addition, we performed clonality studies on different cell lineages in four of these patients applying the RAS mutation, the karyotype and X-chromosome inactivation patterns as clonal markers. Erythroid cells carried mutant RAS, indicating clonal origin. In EBV B cell lines, one of three patients studied harbored a RAS mutation, while the other two patients had polyclonal B cells with wildtype RAS. T lymphocytes were examined in one patient; they were polyclonal and had wild-type RAS. It is likely that JMML is a heterogeneous disease with respect to clonal involvement of different lineages.
The tyrosine kinase inhibitor STI571 is a novel promising class of anticancer drugs. We report a case of cutaneous adverse reactions to STI571 in a young woman with blast crisis of chronic myeloid leukemia. She had first typical acute generalized exanthematous pustulosis mimicking mercury rash and then urticarial eruption. We suggest that cell pathways mediated by some tyrosine kinases might be involved in the pathogenesis of these skin eruptions.
We describe 3 episodes of microangiopathic hemolytic anemia (MAHA) in 2 solid organ recipients under FK506 (tacrolimus) therapy. In both cases, discontinuation of FK506 and treatment with plasma exchange, fresh frozen plasma replacement, corticosteroids, aspirin, and dipyridamole led to resolution of MAHA. In one patient, reintroduction of FK506 led to rapid recurrence of MAHA. FK506-associated MAHA is probably rare but physicians must be aware of this severe complication. In our experience and according to the literature, FK506 does not seem to cross-react with cyclosporin A (CyA), an immuno-suppressive drug already known to induce MAHA.
Microcytosis is a highly prevalent finding during blood examination. This study investigates the causes of microcytosis (defined as mean corpuscular volume (MCV)<82 fl) in 466 patients referred to our laboratory for suspected hemoglobinopathy. The following data were obtained: Hb, MCV, serum iron, transferrin, ferritin, HbA2, HbF, isoelectric focusing of the Hb, gene mapping of chromosome 16 with Xba I and Bgl II and hybridization with an α‐ and a ζ‐probe, inflammatory status. Results show that iron deficiency remains the first cause of microcytosis (35.2% of our patients), even in a selected population such as ours. Deletional α‐thalassemia, probably the most frequent hemoglobinopathy throughout the world, represents the second most frequent cause of microcytosis (31.1%), followed by β‐thalassemia heterozygous state (18.9%). Of our patients, 1.3% had microcytosis due to the presence of an abnormal hemoglobin (HbC, Hb S/C, HbE). Three cases (0.6%) had other possible causes of microcytosis. Of the remaining 60 cases, 28 had an inflammatory state. Finally, 32 cases (6.9%) remain unexplained; taking into consideration the origin of these cases, their hematological parameters and their family history, we postulate that these cases are at high risk for non‐deletional α‐thalassemia.
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