Normal thrombopoietin and its receptor (c-mpl) genes in children with essential thrombocythemia.

BACKGROUND: Following the observation of thrombopoietin (TPO) gene abnormalities as the cause of familiar cases of thrombocythemia similar derangements of TPO and/or its receptor (c-mpl) might be surmised to be at the root of increased platelet count also in non-familiar (sporadic) cases. Although this was not demonstrated in adults, little data exist about childhood. PROCEDURES: We studied the molecular biology of TPO and c-mpl in seven children with non-familiar essential thrombocythemia (ET) and one child with secondary thrombocytosis (ST). Plasma TPO content was measured using a commercially available kit. Genomic DNA was extracted from whole blood by standard methods and TPO and c-mpl genes were amplified by polymerase chain reaction (PCR) and sequenced. RESULTS: Plasma TPO levels were normal in all our patients. No alteration was detected in either coding region, including the flanking intronic sequences of TPO and c-mpl genes. As compared to the published normal sequence of the TPO gene, one allelic base change in a non-coding region of intron 1 was found in all children with ET and ST, but this was reported as a common finding in normal subjects as well. CONCLUSIONS: High platelet count in our series of sporadic ET of childhood is not due to an abnormality either of TPO or c-mpl gene.