GATA1 Mutations in Transient Leukemia and Myeloid Leukemia in “Down” Syndrome.

Introduction: Newborns with trisomy 21 have a 5 to 10% risk to develop transient leukemia (TL). More than 20% of these infants progress to myeloid leukemia of Down syndrome (ML-DS) within the first 4 years of life. Mutations of the hematopoietic transcription factor GATA1 have been identified in almost all patients with TL and ML-DS. Here we report the biological and follow up data of a large cohort of children with proven GATA1 mutation reported to date either as TL (n=43) or ML-DS (n=28).

Results:GATA1 mutations (point mutations, insertion, deletion, duplication; including 45 mutations not yet published) were identified in 42/43 TL (98%) and in 23/28 ML-DS (83%) patients.

In 9 patients multiple mutations were noted in the same clone as confirmed by subcloning. In one patient with TL two different GATA1 mutations were detected in two independent clones. When this patient progressed to ML-DS only the minor clone was present. The majority of the mutations was localized in exon 2 (n=59). Only a few mutations could be found in intron 1 and 2 (n=5) or in exon 3 (n=1). As a result, these mutations led to the introduction of a premature stop codon within exon 2 (n=40), frameshift (n=14), altered splicing (n=7), or lack of an initiation codon (n=4). Interestingly, children with TL and splicing mutations were significantly older at diagnosis than patients with other mutations (day 38 vs. day 3 p <0.05). No differences between mutational types were evident regarding gestational age, white blood cell count, platelet count, hemoglobin levels, or risk of death or ML-DS.

In children with a myeloproliferative disease (MPD; n=7) or acute megakaryoblastic leukemia (AMKL; n=1) without stigmata of Down syndrome, GATA1 mutations could be detected. All of them were diagnosed as trisomy 21 mosaic. In this group the frequency of frameshift and altered splice mutations (5/7 vs. 9/36) was significantly higher compared to those with premature stop codons (2/7 vs. 27/36); p_{Fishers exact} =0.03).

In 20 children (TL n=13, ML-DS n=7) the GATA1 mutant clone has been prospectively monitored by quantitative PCR using patient specific TaqMan probes. Seventeen TL patients showed decreasing minimal residual disease (MRD) levels and became negative (<10⁻⁴) during follow-up, whereas three children, who later developed ML-DS, remained positive at all time points. After two treatment elements all ML-DS patients had undetectable levels of GATA1s. After a median follow up of 1.5 years (0.9 to 2 years), no child suffered relapse however, the follow-up is much too short to draw definitive conclusions.

Conclusion: In conclusion, we confirmed the high frequency of GATA1 mutations in children with TL or ML-DS. The occurrence of splicing mutations correlated with the age at diagnosis underlining the biologic relevance of the kind of mutation. We demonstrated the feasibility of a leukemia specific monitoring of MRD. As those children with sustaining detectable levels of GATA1s progressed to leukemia, these results might have therapeutic consequences for TL and later for ML-DS. In addition it may serve as a proof of principle for the feasibility of MRD monitoring in other AML-associated mutations. The identification of GATA1s positive MPD and AMKL in children without obvious stigmata of Down syndrome, all confirmed as trisomy 21 mosaic, implicate the necessity of GATA1s diagnostics in all newborn and infants with megakaryoblastic leukemia.