Mutations in exon 2 of GATA1 are early events in megakaryocytic malignancies associated with trisomy 21

Abstract

Patients with Down syndrome (DS) frequently develop 2 kinds of clonal megakaryocytosis: a common, congenital, spontaneously resolving, transient myeloproliferative disorder (TMD) and, less commonly, childhood acute megakaryoblastic leukemia (AMKL). Recently, acquired mutations in exon 2 of GATA1, an X-linked gene encoding a transcription factor that promotes megakaryocytic differentiation, were described in 6 DS patients with AMKL. The mutations prevent the synthesis of the full-length GATA1, but allow the synthesis of a shorter GATA1 protein (GATA1s) that lacks the transactivation domain. To test whether mutated GATA1 is involved in the initiation of clonal megakaryoblastic proliferation or in the progression to AMKL, we screened 35 DS patients with either AMKL or TMD and 7 non-DS children with AMKL for mutations in exon 2 of GATA1. Mutations were identified in 16 of 18 DS patients with AMKL, in 16 of 17 DS patients with TMD, and in 2 identical twins with AMKL and acquired trisomy 21. Analysis revealed various types of mutations in GATA1, including deletion/insertions, splice mutations, and nonsense and missense point mutations, all of which prevent the generation of full-length GATA1, but preserve the translation of GATA1s.We also show that the likely mechanism of generation of GATA1 isoforms is alternative splicing of exon 2 rather than, or in addition to, alternative translation initiation, as was proposed before. These findings suggest that acquired intrauterine inactivating mutations in GATA1 and generation of GATA1s cooperate frequently with trisomy 21 in initiating megakaryoblastic proliferation, but are insufficient for progression to AMKL. (Blood. 2003; 102:981-986)

Abnormalities of GATA-1 in Megakaryocytes from Patients with Idiopathic Myelofibrosis

“…The expression of the two human GATA-1 mRNA transcripts was assessed by reverse transcriptase (RT)-PCR, starting from 200 ng of cDNA, using a forward primer from exon 1 and a reverse primer from exon 3 ( Table 2). 36 Amplification was performed at 63°C in a GeneAmp 9700 Perkin-Elmer thermocycler and samples were analyzed after 25, 28, 31, and 33 cycles to be in the linear range of amplification. Positive and negative controls were included in each experiment.…”

Evolution of myeloid leukemia in children with Down syndrome

“…GATA1 somatic mutations, first identified from a small series of ML-DS patients [34], are present in blast cells both in DS neonates with TAM and children with ML-DS [34][35][36][37][38]. GATA1 mutations disappear when TAM/ML-DS enters the remission phase, indicating that these are acquired events [35].…”

“…Estimates of the risk of ML-DS following TAM vary from ~5 % in the recent prospective study to 30 % in retrospective studies of clinically diagnosed TAM [8,11,40], and analysis of paired samples from the same patient found the identical GATA1 mutation in both pre-leukemic (TAM) and leukemic (ML-DS) stages [11,37,43].…”

Of mice and Down syndrome

“…[1][2][3] Sequence alterations in the region encoding the N-terminal activation domain of GATA1 include insertions, deletions, missense, nonsense, and splice-site mutations at the exon 2/intron boundary, resulting in the synthesis of a short-form GATA1 (GATA1s; 40-kDa) protein that exhibits altered transactivation capacity compared with the 50-kDa wild-type protein. GATA1 mutations are believed to represent early or initiating "genetic hits" in a multistep process of leukemogenesis in Down syndrome that can begin prenatally.…”