Clonality analysis of hematopoiesis in essential thrombocythemia:
advantages of studying T lymphocytes and platelets
N el-Kassar, G Hetet, J Briere and B Grandchamp
INSERM U409, Faculte de Medecine Xavier Bichat, Paris, France.
Essential thrombocythemia (ET) is a myeloproliferative disorder
characterized by a sustained elevation of the platelet count in the absence
of other causes of thrombocytosis. ET is difficult to diagnose, and the
demonstration of clonal hematopoiesis may be of value. However, clonality
analysis of hematopoietic cells based on the study of the X- chromosome
inactivation pattern is complicated by the observation that some normal
females present skewed lyonization. Moreover, DNA methylation of X-linked
genes in hematopoietic cells may differ from that in other tissues.
Appropriate controls for skewed lyonization are therefore critical for the
study of clonality. We developed two techniques based on X-chromosome
inactivation and polymerase chain reaction (PCR) analysis of polymorphisms,
to study clonality in ET patients. Reverse transcriptase-PCR analysis of
IDS, P55, and G6PD mRNAs was used to examine the different hematopoietic
cell lineages including platelets in patients heterozygous for these
polymorphisms and analysis of the HUMARA gene methylation pattern permitted
us to study clonality in all nucleated cell fractions of the other
patients. Using both types of assay and T lymphocytes as a control tissue
for lyonization, clonal hematopoiesis was demonstrated in 28 patients. In
14 patients, the granulocytes were polyclonal; among these patients,
platelets were monoclonal in 3 cases, polyclonal in 7 cases, and in the
remaining 4 cases this fraction could not be studied because the patients
were homozygotes for all RNA markers. No conclusion about clonality could
be drawn in 6 cases. Polyclonal hematopoiesis was found in all the cases of
reactive thrombocytosis. These findings confirm the high frequency of
monoclonal hematopoiesis in ET, the utility of studying platelets, and the
possibility of using T lymphocytes as a control tissues for X-chromosome
inactivation patterns.
Volume 89,
Issue 1,
pp. 128-134,
01/01/1997
Copyright © 1997 by The American Society of Hematology
