GATA1 Mutations in Clonal Disorders of Children with and without Down Syndrome.

Down Syndrome (DS) children are 10–20 times folder likely to develop acute leukemia (AL) within the first four years of life compared to general pediatric population. Recently acquired somatic mutations in GATA1 gene on chromosome X have been described in most cases of DS AML and congenital TMD of DS carry the same type of mutations in exon 2 of GATA1. Here we report the preliminary results of GATA1 mutation in AL with and without DS children. The aim of this study is to provide insights in the relationships of GATA1 mutations and trisomy 21 in leukemogenesis process. GATA1 mutations were assayed in genomic DNA in 34 children with DS and AL, 2 with transient myeloproliferative disorder (TMD), 3 with myelodisplastic syndrome. Sequential sample including 2 pre-diagnosis in neonate period and 1 year before diagnosis were available in two children and 40 randomly selected DS children without known hematological disorder. A rare case of a non-DS neonate with TMD and clonal trisomy 21 were also examined. Genomic DNA was extracted and the exon 2 of GATA1 was PCR amplified as described by Wechsler et al. PCR products were sequenced in both directions and analyzed in a MegaBACE 1000 automated sequencer. Presently, GATA 1 mutations were found in 7 cases of AL, in all TMD cases with DS and none MDS case of DS. Interesting, a neonate girl with no phenotypic features of DS, but TMD features whose karyotype revealed 47, XX, +21/46, XX mosaics. A G-to-T transversion was detected which is predicted to result in a premature stop codon (c.119G>T; p.Glu67X) at the time of onset of TMD. However this same mutation was not detcted at 5 years of age.To our knowledge, this is the first reported case of TMD without DS with a detected GATA1 mutation. The presence of both somatically acquired abnormalities probably confers a proliferative advantage to the cell, resulting in TMD. We postulated in this case that both genetic abnormalities were temporary because of the non self-renewing nature of the progenitor that first had a non-disjunction event and this progenitor and the proliferative clone eventually disappeared. Therefore, even the proliferative advantage that the combination of trisomy 21 and GATA1 mutation confer, maintenance of these genetic changes are necessary for full leukemic transformation and persistence.