Pediatric Essential Thrombocythemia (ET): Evaluation of Clonality Status.

ET is a very rare disease in pediatric age and some evidence suggest that ET in childhood may be a possible variant of the ET as described in adults. Clonal assays using X chromosome inactivation patterns (XCIPs) have been used to demonstrate the clonal origin of ET. However, about half women with ET seem to have a polyclonal XCIPs and the occurrence of thrombosis seems to be higher in patients with monoclonal XCIPs. We report 7 females in pediatric age affected with ET (mean age at diagnosis 9 years). The diagnosis of ET was made in agreement with the Polycythemia Vera Study Group Criteria. The main clinical data of our children are summarized in the table. None of the children had heavy haemorrhages nor splenomegaly. HUMARA trinucleotide repeated polymorphism in granulocytes DNA amplified using two primers flanking the STR, was used to assess myeloid clonality of our patients. The PCR products will be quantified after electrophoresis with density analysis. T lymphocytes DNA of the patients were also tested for the HUMARA polymorphism as control. Monoclonal granulocytes XCIPs was demonstrated in only 1 asymptomatic child who had polyclonal T-lymphocytes, while 5 other children had polyclonal XCIPs of both granulocytes and T-lymphocytes. Omozygous XCIP of 1 chlid did not permit clonality evaluation.

In conclusion, as observed in adults, also children with ET seem to be heterogeneous concerning clonality status. The percentage of polyclonal cases seem to be higher in pediatric age if compared with adults (data of the literature). The sole patient with a major thrombotic complication is polyclonal. Again pediatric ET seems to be different than adults ET: more studies are needed to clarify the biological characteristics of pediatric ET