Genetic Mutation in Cytopenic Patients: Distinctive Genomic Profile between Preclinical Vs. Clinical Myelodysplastic Syndrome

Genetic mutation in cytopenic patients: Distinctive genomic profile between preclinical vs. clinical myelodysplastic syndrome.

Introduction

Myelodysplastic syndromes (MDS) are heterogeneous groups of clonal hematopoietic disorders. The current diagnosis of MDS is based on morphologic assessments of dysplasia which are subjected to inter-observer variability and cytogenetic abnormalities which are frequently absent. Somatic mutations in myeloid-related genes have been identified in MDS. However, they are also found in idiopathic cytopenia of unknown significance (ICUS) that shows no significant dysplasia. Therefore, we aimed to explore the clinical implications of genetic mutations in ICUS and compared with MDS. The secondary objective was to find association between degree of dysplasia and somatic mutations.

Materials and Methods

The patients with peripheral cytopenia ≥1 lineage (ANC < 1,800/mm³, hemoglobin < 10 gm/dL, platelet < 100x10⁹/mL) without explainable causes were enrolled. Bone marrow aspirates were evaluated independently by 2 hematologists. Of note, dysplasia are defined by WHO 2008 classification (eg. Erythroid lineage: ring sideroblasts, megaloblastoid change; granulocytic lineage: hypogranularity, pseudopelger-huet anomaly; megakaryocytic lineage: hypolobate, micro-megakaryocyte). The significant dysplasia cut off was 10% in single lineage or more. If there was a discrepancy, the third hematologist would help to reach the final consensus. We extracted DNA from bone marrow and performed next generation sequencing (NGS) that targeted 143 myeloid-related genes.

Results

Forty-eight patients were enrolled in this study. The median age at diagnosis was 70 years (71-96). Results of bone marrow examinations were categorized by morphology into 3 groups; non-significant dysplasia (dysplasia < 10%) 27%, low risk MDS (IPSS-R ≤3.5) 42% and high-risk MDS/sAML (IPSS-R >3.5/Blast≥20% in BM or peripheral blood) 31%. Most of cases (77%) carried normal cytogenetics while other genetic alterations were complex chromosome (6%), -Y (6%), del(5q) (4%), trisomy 8 (2%), del(20q) (2%), i(17q) (2%). Thirty from 48 cases (62%) harbored more than 1 somatic mutation. Twenty-eight gene mutations were identified. Mutations were detected 1.6 mutation per 1 patient in average. Most frequent somatic mutations were ASXL1:10/80 (12%), TET2:9/80 (11%), MFDS11: 6/80 (7%), TP53:6/80 (7%), and RUNX1:5/80 (6.25%). The proportions of cases with somatic mutations were not different across the groups (no dysplasia 50%, non-significant dysplasia 80% and significant dysplasia 62%). According to mutation types in each group, mutations in epigenetic pathways were the most frequent mutations across all patient subgroups (ICUS 64.7%, low-risk MDS 51.8 %, and high-risk MDS 52.5%). Mutations in transcription factor were predominated in MDS (18.5% and 25.0% in low-risk and high-risk MDS, respectively) compared to ICUS (11.7%). Individual average frequency of gene mutations was significantly different between disease subtype (high risk MDS 2.7 gene/person, low risk MDS 1.1 gene/person, ICUS 1.3 gene/person (P=.038). Higher variant allele frequency (VAF) of mutated genes was significantly observed in high risk MDS (38.3%) compared to low risk MDS (30.8%) and preclinical MDS (29.0%) (P=.03).

Conclusion

In conclusion, molecular profiling was significantly different between preclinical MDS and MDS groups in terms of types of somatic mutations and VAF. This unique contrast could be used to distinguish between preclinical MDS and clinically significant MDS. In contrast, degree of marrow dysplasia was not associated with number of gene mutations in this study. Prediction for clinical consequent of somatic mutations in CCUS requires long term follow up.

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