ABSTRACT
BACKGROUND: Essential thrombocythemia (ET) rarely occurs in the pediatric population and little is known about the clinical course and the molecular characteristics. PROCEDURE: In this retrospective multi-institutional study we examine the clinical, hematological, and molecular features of 12 children aged 5-16 years with thrombocytosis and a suspected diagnosis of ET. RESULTS: Median follow-up was 59 months (range 10-72). Seven patients presented with clinical symptoms potentially related to thrombocytosis. The remaining five patients were diagnosed incidentally. Median platelet count at diagnosis was 1,325 x 10(9)/L (range 600-3,050). In 11 out of 12 cases bone marrow morphology was consistent with ET, the remaining patient had chronic idiopathic myelofibrosis. Cytogenetic analyses were normal in all studied cases and only one out of nine analyzed cases harbored a JAK(V617F) allele. Within 6 months after initial presentation one patient who was initially asymptomatic developed thrombosis and another patient had mild bleeding. Eight patients were treated with acetylsalicylic acid, one patient received hydroxyurea, and two patients received anagrelide. At last follow-up, all patients were alive and none had developed leukemia. Five patients experienced hematological remission. Two children had not received any therapy. During the course of their disease, nine patients developed symptoms possibly attributable to an elevated platelet count. CONCLUSIONS: In JAK2 mutation negative cases, long-term follow-up is helpful to distinguish between primary and secondary thrombocytosis. Secondary cases are not associated with organomegaly but may present with unspecific symptoms. Indications for treatment in children remain unclear.
Subject(s)
Primary Myelofibrosis/diagnosis , Thrombocythemia, Essential/diagnosis , Adolescent , Age Distribution , Child , Child, Preschool , Chronic Disease , Female , Humans , Janus Kinase 2/genetics , Janus Kinase 2/metabolism , Male , Primary Myelofibrosis/therapy , Retrospective Studies , Thrombocythemia, Essential/therapy , Time FactorsABSTRACT
Noonan syndrome (MIM 163950) is characterized by short stature, facial dysmorphism and cardiac defects. Heterozygous mutations in PTPN11, which encodes SHP-2, cause approximately 50% of cases of Noonan syndrome. The SHP-2 phosphatase relays signals from activated receptor complexes to downstream effectors, including Ras. We discovered de novo germline KRAS mutations that introduce V14I, T58I or D153V amino acid substitutions in five individuals with Noonan syndrome and a P34R alteration in a individual with cardio-facio-cutaneous syndrome (MIM 115150), which has overlapping features with Noonan syndrome. Recombinant V14I and T58I K-Ras proteins show defective intrinsic GTP hydrolysis and impaired responsiveness to GTPase activating proteins, render primary hematopoietic progenitors hypersensitive to growth factors and deregulate signal transduction in a cell lineage-specific manner. These studies establish germline KRAS mutations as a cause of human disease and infer that the constellation of developmental abnormalities seen in Noonan syndrome spectrum is, in large part, due to hyperactive Ras.
