Acute Megakaryoblastic Leukemia Without GATA1 Mutation After Transient Myeloproliferative Disorder in an Infant Without Down Syndrome

Case Report

A 7-week-old full-term infant girl with unremarkable perinatal history was referred to our hospital for a 5-day history of hematochezia and mild epistaxis. Physical examination showed hepatosplenomegaly, scattered petechiae, and grossly bloody stool. No phenotypic features of Down syndrome (DS) were noted. CBC showed elevated WBC (51.2 × 10⁹/L) with 10% blasts, anemia (7.1 g/dL), and thrombocytopenia (54 × 10⁹/L). Bone marrow aspirate (BMA) showed hypercellularity, increased megakaryoblasts (15%), and dysplastic megakaryocytes (Fig 1A). Flow cytometric analysis showed expression of megakaryocyte-specific membrane markers (CD41, CD42b, and CD61) but not myeloperoxidase in blasts. Cytogenetic analysis revealed karyotype 47,XX,+21[16]/46,XX [4] (Fig 2A, arrow indicates trisomy 21). Fluorescence in situ hybridization using ETO-AML1 probes showed a normal pattern of signal distribution in buccal epithelial cells, without evidence of an extra AML1 signal. There was a single base pair deletion of G at nucleotide 150 (relative to ATG) in GATA1 exon 2 in megakaryoblasts (Fig 3, arrow). The patient was diagnosed with transient myeloproliferative disorder (TMD) and became transfusion independent 1 month later. Peripheral blood blasts disappeared within 3 months without administration of chemotherapy.

Fig 1.

Fig 2.

Fig 3.

At 7 months of age (5 months postpresentation), the patient again developed hematochezia and thrombocytopenia (10 × 10⁹/L). WBC was 9.7 × 10⁹/L with 1% circulating blasts, and hemoglobin was 10.5 g/dL. BMA revealed marked megakaryocytic dysplasia and increased megakaryoblasts (34%; Fig 1B). The blast population expressed megakaryocyte-associated antigens similar to those seen in the TMD sample but lost expression of CD56 and CD8 and showed weaker CD117 expression. Cytogenetic analysis revealed karyotype 47,XX,+21[14]/47,idem,del(5)(p13) [3]/46,XX [8] (Fig 2B, vertical arrow indicates trisomy 21 and horizontal arrow shows a deletion of 5p). FISH using a 5p subtelomeric probe showed an interstitial deletion [del(5)(p13p15)] (arrow, Fig 4). Given these clinical and laboratory findings, the patient was diagnosed with acute megakaryoblastic leukemia (AMKL).

Fig 4.

The patient was enrolled onto the multi-institutional protocol AML02 (A Collaborative Trial for the Treatment of Patients With Newly Diagnosed Acute Myeloid Leukemia or Myelodysplasia).¹ Therapy consisted of standard doses of two courses of remission induction (cytarabine, daunomycin, and etoposide) and two courses of consolidation (cytarabine and mitoxantrone, and cytarabine and L-asparaginase). She had a complete response (negative minimal residual disease) to the first course of remission induction and tolerated chemotherapy well. The third dose of consolidation therapy was not administered because of refractoriness to platelet transfusions associated with development of platelet antibodies. She has been off therapy for 18 months and remains in complete remission. Cytogenetic analysis in remission marrow showed 46,XX. Retrospective analysis of GATA1 gene using a BMA sample at onset of AMKL did not show any mutations with sequence of 30 clones.

Discussion

TMD, characterized by clonal proliferation of megakaryoblasts, develops almost exclusively in patients with DS during the neonatal period.^2,3 The reported incidence of TMD in patients with DS is 10% but may actually be higher because some affected fetuses die in utero. TMD usually resolves spontaneously within 2 to 3 months, but 20% to 30% of patients develop overt AMKL 1 to 30 months post-TMD. TMD also occurs in children without DS who have either mosaicism for trisomy 21 or normal karyotype.⁴ The frequency and pathogenesis of TMD and subsequent AMKL in these children is not well known because TMD may go undetected.

Classic TMD in DS is characterized by elevated WBC (median, 47 × 10⁹/L; range, 5 to 380 × 10⁹/L) with varying percentages of circulating blasts.^2,3 BMA usually reveals dysplastic megakaryocytes and megakaryoblasts that are typically negative for myeloperoxidase and express megakaryocytic markers (CD41, CD42b, and CD61). In both patients with DS and those who are phenotypically normal, blast cells show trisomy 21. Hematopoietic cells in TMD also have acquired mutations in transcription factor gene GATA1 (Xp11.23), which controls erythropoiesis and megakaryopoiesis.⁵ The mutation, seen exclusively in exon 2, leads to truncated protein GATA1s, which lacks the N-terminal transactivation domain but is not leukemogenic in the absence of trisomy 21.⁶ The combination of GATA1s and trisomy 21 seems to confer a selective advantage to blasts. Mortality rate from TMD- and DS-associated complications (eg, liver failure, congestive heart failure, renal failure, disseminated intravascular coagulation, hyperleukocytosis, and/or sepsis) can be 10% to 20%.^2,3 Our patient did not have a DS phenotype, and bleeding tendency was controlled by platelet transfusions only. The initial sole cytogenetic abnormality of trisomy 21 in leukemic blasts prompted us to analyze the GATA1 mutation, which confirmed diagnosis of TMD. Cytogenetic analysis of somatic cells (eg, buccal mucosa and skin fibroblasts) is necessary to rule out DS as well as its mosaicism; in our patient, analysis of buccal mucosa and remission marrow ruled out mosaicism.

WBCs in patients with DS with AMKL and history of TMD (median, 10 × 10⁹/L; range, 1.8 to 40.6 × 10⁹/L) are lower than in those presenting with TMD, but BMA examinations are indistinguishable, and GATA1 mutations are seen in both cases.^2,3 Because not all patients with TMD progress to development of AMKL, additional genetic or epigenetic events are likely required for progression to overt leukemia. Altered telomerase activity, TP53 mutations, and additional acquired karyotype abnormalities (eg, +8, −7, and −5/5q−) have been reported.⁷ A retrospective review reported that five of 16 patients with TMD without DS developed subsequent leukemia, three developed AMKL, and two developed non-AMKL acute myeloid leukemia, but patients were not checked for the presence of GATA1 mutations.⁴

Our patient developed AMKL subsequent to TMD. She had high WBC with TMD, spontaneous remission, and reappearance of megakaryoblasts with lower WBC. Acquisition of an additional karyotypic abnormality—del(5p)—and development of several immunophenotypic shifts with progression to AMKL suggest that a subclone of TMD cells evolved and acquired selective advantage. Most likely, GATA1 mutation was lost with AMKL.

Event-free survival is more than 80% for patients with DS with AMKL but less than 50% in patients without DS with AMKL.^2,3 In in vitro studies, AMKL blasts from patients with DS are more sensitive to chemotherapeutic agents, especially cytarabine, than those from patients without DS because of overexpression of the cystathionine β-synthase gene (localized to 21q22.3) and low expression of cytidine deaminase with GATA1 mutation.^8,9 Conventional AMKL therapy in patients with DS is associated with high treatment-related mortality.¹⁰ Thus, several collaborative study groups have adapted their standard AMKL protocol for patients with DS by reducing chemotherapy doses or prolonging intervals between courses. Our patient received standard doses of chemotherapy because we initially considered that the regimen would be well tolerated in a patient with no evidence of constitutional chromosomal abnormalities and efficacious against leukemia cells with acquired +21. This regimen seemed appropriate because GATA1 mutation was absent in AMKL sample. Although such cases are rare, our case illustrates that the treatment regimen for AMKL preceded by TMD in non-DS children must be carefully selected. Efficacy of a DS-based reduced-intensity regimen for those who retain GATA1 mutation remains to be determined.

AUTHORS' DISCLOSURES OF POTENTIAL CONFLICTS OF INTEREST

The author(s) indicated no potential conflicts of interest.