Mutations In GATA2 Are Rare In Juvenile Myelomonocytic Leukemia

Germline mutations in GATA2, a gene that encodes for transcription factors involved in hematopoiesis and vascular development, have recently been described in MonoMAC syndrome, Emberger syndrome and in select cases of mild chronic neutropenia. These disorders are unified by their predisposition to myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML). Patients with MonoMAC syndrome have also been noted to display monosomy 7 in their bone marrows in up to 50% of cases. Overexpression of GATA2 due to somatic mutations in cases of de novo pediatric AML, has also been shown to be a negative predictor of outcome.

Juvenile myelomonocytic leukemia is a rare childhood malignancy with overlapping features of MDS and myeloproliferative neoplasm (MPN) that can transform to AML and is characterized by hyperactive RAS signaling. Mutations in NF1, NRAS, KRAS, PTPN11, and CBL are found in 85-90% of newly diagnosed patients, and monosomy 7 is the most common recurrent karyotypic abnormality seen in JMML. We therefore hypothesized that mutations in GATA2 may play a role in the development of JMML.

Samples from 57 patients with JMML were screened for GATA2 mutations. Patient samples and clinical data were collected from the Children's Oncology Group (COG) trial AAML0122. DNA was extracted as per previous protocols from peripheral blood or bone marrow and whole genome amplified using Qiagen REPLI-g kit according to manufacturer specifications. We performed bidirectional Sanger sequencing (Beckman Coulter Genomics) of the entire coding region of GATA2 (NM_001145661.1) and aligned the sequences using CLC Workbench software (CLC Bio, Aarhus, Denmark). Only missense, splice site or nonsense mutations were evaluated using SIFT (Sorting Tolerant From Intolerant) to predict the impact on the structure and function of identified mutations on the protein.

Patient J384 was found to have a nonsense point mutation at c.988C>T (R330X) in the N-terminal region of the zinc finger portion of the protein (Figure 1a). This hotspot mutation has been reported in several patients with mild chronic neutropenia who displayed a predisposition to developing MDS and AML. The patient was also found to have a missense point mutation at c.962T>G (L321R) predicted to be damaging by SIFT. Subcloning of the gene using a TA cloning kit with pCR 2.1 vector (Invitrogen), followed by direct sequencing of individual colony picks, revealed that the two sequence variants only occurred in a trans configuration. Out of 40 amplicons sequenced, 20 were found to have the c.988C>T transition, 16 were found to be have the c.962T>G variant, and four were found to be wild type. We therefore hypothesize that the c.988C>T was inherited as a germline event and that c.962T>G was somatically acquired in the majority of the remaining wild type alleles. No other point mutations or insertions/deletions were discovered in this cohort.

Figure 1

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Identification of 2 distinct GATA2 mutations in patient J384.

Figure 1

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Identification of 2 distinct GATA2 mutations in patient J384.

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This patient was previously identified to have a KRAS G12D mutation (c.35G>A) as well as monosomy 7. This patient died prior to undergoing transplant within months of diagnosis. While the patient technically met criteria for the diagnosis of JMML, it should be noted there were several atypical features, including older age at diagnosis (4 years and 10 months), and absence of hypersensitivity in myeloid progenitor cells to the cytokine granulocyte–macrophage colony stimulating factor (GM-CSF) in colony assay. This raises the possibility that patient J384 actually had MonoMAC syndrome with MDS and not JMML.

This represents the first description of a GATA2 mutation in a patient suspected of having JMML. To our knowledge, this is the first report of a biallelic mutation in GATA2, combining a germline mutation with somatic acquisition. In addition, MonoMAC syndrome has not been reported to be associated with KRAS mutations to date. GATA2 mutations should therefore be considered in patients with atypical features of MDS or JMML.

Panel (a) Bidirectional sequencing of patient sample J384 revealed two distinct sequence variants in both the forward (shown here) and reverse strands. Panel (b) Sequencing of 40 individual colony picks revealed that each sequence variant occurred in a trans configuration (CP 9 and CP13 are shown here as examples). In addition, 10% of colony picks (i.e. CP 32) revealed a wild type sequence, indicating that at least one of the two variants was a somatic event.